Oops! Yeah that's correct. My bad.

Chữ Khoa Đẩu ‧字蝌蚪
Chữ Hán ‧字漢
Chữ Nho ‧字儒
Chữ Nôm ‧字喃
Chữ Quốc Ngữ ‧字國語

In Vietnamese, the 字 precedes the style it represents, not after the definition of style.

Why does the word for "Wednesday", <thứ tư>, use the Sino-Vietnamese word for "four" when the rest of the days use native Vietnamese numbers?

That is a valid question which I have asked myself many times and, am seeking Vietnamese scholars upon this mystery. Before I have any solid answers, my own personal guess is that, the Chinese pronounciation of that era (or dialect) which influenced Vietnamese sounds close to the native Vietnamese number for "four", and thus, the original Chinese character is retained as it is.

That is a rather observant question! Firstly, the Vietnamese count their days of the week rather than assigning specific names to them (except for Sunday). However, maybe due to the influence of early European missionaries themselves, the first day of the week is actually Sunday with Monday being the 2nd, Tuesday the 3rd etc. With the exception of Sunday (Chủ nhật = the primary day, or the day of the lord) the rest of the days are given a number from 2 to 7 (Monday to Saturday).

Sunday = Chủ nhật
Monday = Thứ hai
Tuesday = Thứ ba
Wednesday = Thứ tư
Thursday = Thứ năm
Friday = Thứ sáu
Saturday = Thứ bảy

Besides Sunday, the only other odd one out SEEMS to be Wednesday. 'Thứ' can mean a type or sort of something but can also mean 'order/rank'. The word thứ in this context may be a contraction of 'ngày thứ' (day number, day order/rank). Generally speaking, the ordinal numbers in Vietnamese are actually: nhất, nhì, ba, tư, năm with the rest of the numbers being the same as the cardinals. The cardinal numbers from 1-5 are: một, hai, ba, bốn, năm. Apart from the two, there is also a rarely used Sino-Vietnamese (Chinese borrowed) number system mostly relegated nowadays to more academic terms.

Number: 1, 2, 3, 4, 5
Cardinal: một, hai, ba, bốn, năm
Ordinal: nhất, nhì, ba, tư, năm
Sino-Viet: nhất, nhị, tam, tứ, ngũ

Technically, if the days of the week are being counted like ordinal numbers, then why is Monday not thứ nhì but rather thứ hai? That is because the cardinal for the number 2 'hai' can also be used colloquially to mean 2nd. Hence, if you factor in that irregularity, you end up with the rest of the numbers, 3-7 being regular. Wednesday is thứ tư instead of thứ bốn because the days are being counted (ordinal numbers).

As to the Chữ Nôm, native Vietnamese numbers were given new characters as shown in the examples VROOR has given. Every number from 1-9 except for 1 and 4 is unique to Chinese. 1 is simply a borrowing of the character 没 which is actually pronounced một in Sino-Vietnamese as well. Similarly, the ordinal number 4 'tư' borrows the character 四 for its rough pronunciation. Of course, as with the number 2 the ordinal number for 4 is a corruption or nativisation of the Chinese. However, you will also see a lot of Chữ Nôm writers use the original simple Chinese number characters to represent native Vietnamese numbers. ie. 一, 二, 三, 四, 五 for một, hai, ba, bốn, năm. Therefore, there could be confusion with the Sino-Vietnamese numbers nhất, nhị, tam, tứ, ngũ but that is quite infrequent.

Vietnamese also count their months in cardinal terms. Tháng (month) + a cardinal number from one to twelve. So once again, month two (February) is Tháng hai instead of Tháng nhì, April is Tháng tư instead of Tháng bốn.



Actually I wrote 漢字, 喃字, 國語字 etc. using the Chinese terms for them, not the Chữ Nôm.

P.S: I'm quite fluent in Vietnamese because I was raised in a Vietnamese family although I'm ethnically 1/2 Chinese.

Thank you for explaining this information.



I was not aware you were using Chinese terms because, the names where given in Vietnamese first; thus, I presumed they were to be in Chữ Nôm. I have no doubts about your linguistic expertise and, my response was not a challenge to you, it was a mere input based upon that mistake (of which, I presumed the terms are Chữ Nôm).

Anyway,

Family

Here's a little list to recount the terms for family and extended family members.
Con - child
Cháu - grandchild
Cha - father (alternatives include ba, bố, tía)
Mẹ - mother (alternatives include má)
Anh - older brother, male of similar age, OTHER* see below
Chị - older sister, female of similar age, OTHER* see below
Em - younger sibling, to be specific: em + trai/gái (boy/girl), OTHER* see below
Chồng - husband
Vợ - wife
Ông - old man[/b]
Bà - old lady
Ông cố/cốc - great grandfather
Bà cố/cốc - great grandmother

Ngoại - mother's side, literally 'outside'
Ông ngoại - mother's father
Bà ngoại - mother's mother
Cô - mother's older sister~
Dì - mother's younger sister
Cậu - mother's brother
Dượng - mother's sister's husband
Mợ - mother's brother's wife

Nội - father's side, literally 'inside'
Ông nội - father's father
Bà nội - father's mother
Bác - father's older brother & his wife
Chú - father's younger brother
Cô - father's sister~
Thím - father's brother's wife
__________________________________________________________________________

From now on I'll add little Culture Notes here and there.
Culture Note: Vietnamese people traditionally live in a household which may include not only your family but members of your extended family. It is not uncommon to see a household in Vietnam with as many as a dozen people. Generally, a child will not move out until they are married.

Lesson
In this lesson, you will learn how to ask questions about others' families as well as responding to questions about your own.

Key Words
tên - name, to be called
là - copula*, to be
gì? - what?
được - to get, to have
có - to have, a yes response to a 'do you or do you not have?' type question
bao nhiêu? - how many?
người - person, people
trong - in, inside, within
gia đình - family
của - possessive, belonging to
còn - to remain, to have remaining
chỉ - only
hơi - quite

Short Conversation
A - Ánh (a female), B - Bình (a female slightly younger than Ánh)

Vietnamese
A - Chào bạn, xin hỏi bạn tên là gì và năm nay bao nhiêu tuổi ạ?
B - Tôi tên là Bình và năm nay được mười chín tuổi, còn bạn?
A - Chị tên là Ánh, năm nay được hai mươi mốt tuổi.
B - Gia đình chị có bao nhiêu người? Của em chỉ có ba người - cha, mẹ và em.
A - Gia đình chị hơi lớn, có tám người - cha, mẹ, hai người anh, một người chị, hai em gái và chị.

English
A - Hi, may I ask your name and how old you are this year?
B - My name is Binh and this year I am eighteen years old, and you?
A - My name is Anh, and this year I am twenty one.
B - How many people are there in your family? Mine only has three people - father, mother and me.
A - My family is quite large, there are eight people - father, mother, two older brothers, one older sister, two younger sisters and me.

*ạ functions to soften the tone of a question. Also, notice how Bình all of a sudden refers to herself as em, similarly Ánh refers to herself as chị upon finding out she is older than Bình.

Culture Note: It is not uncommon to have someone who you have met for the first time ask about your age. This is not considered rude as they are merely trying to figure out how to address you properly.

It probably comes from Portuguese. In Portuguese the days are also numbered but until Saturday:
Sunday = domingo (day of the Lord)
Monday = segunda-feira (2nd fair)
Tuesday = terça-feira (3rd fair)
Wednesday = quarta-feira (4th fair)
Thursday = quinta-feira (5th fair)
Friday = sexta=feira (6th fair)
Saturday = sábado (Shabbat)

I think you mean to say Sabbath - Shabbat refers specifically to the Jewish version of the holiday.