One Hawaiian word that is used in English is a’a, which is defined as “a kind of rough-surface volcanic rock” [source].
However in Hawaiian it is written ʻaʻā, pronounced [ʔəˈʔaː] and means:
1. to burn, blaze, glow; fire; staring (eyes)
2. lava; stony, abounding with ʻaʻā lava
3. Sirius (the star)
4. young stage of damselfish
The word aʻa [əˈʔa] means:
1. small root, rootlet, vein, artery, nerve, tendon, muscle
2. to send greetings or love; joyous hospitality; joy at greeting a loved one
There is also ʻaʻa [ʔəˈʔa], which means:
1. to brave, dare, challenge, defy, check, venture; to accept a challenge; to volunteer; to act wickedly or presumptuously; bold, venturesome, valiant, intrepid
2. belt, girdle, waist; to gird, to tie on
3. bag, pocket, caul, envelope for a foetus, scrip; fiber from coconut husk; clothlike sheath at base of coconut frond; cloth; chaff, hull
4. a wind
5. booby bird
And ʻā.ʻā [ʔaː.ʔaː], which means:
1. dumbness, inability to speak intelligibly, a dumb person; dumb, silent, still; to stutter and stammer, as a dumb person
2. dwarf, small person; dwarfish, small
3. demented, panic-stricken
4. booby bird.
5. male ʻōʻō bird
Source: Hawaiian Dictionaries
This shows the importance of the ʻokina (“cutting”) and kahakō (“long mark”) in Hawaiian. The former represents a glottal stop [ʔ] and is a letter in Hawaiian, and the latter indicates a long vowel.