I learnt a useful Czech expression today – souhlasím – which means ‘I agree; all right; ok(ay)’. The element hlas (voice; sound; vote) I recognise, and I guessed that the prefix sou- might mean together, or something similar.
According to Wiktionary, sou- is akin to the English prefix co- (together, mutually, jointly), so souhlasím might be literally translated as ‘I together-voice’ or ‘I with-voice’.
Examples of usage and related expressions:
– souhlasím s tebou – I agree with you
– souhlasím s dlouhou procházkou – I am quite game for a long walk
– souhlas = agreement; consent; acceptance; approval; consensus
– souhlasit (s) – to agree (with); approve; concure; assent; go along (with)
– souhlasící = agreeable; congruous; consentaneous
Sources: slovnik.cz, bab.la Dictionary
Russian has an analogous construct, referring to agreement as being of common voice: Согласие, or the concept of “agreement”. There are several related terms such as согласный (in agreement), соглашение (an actual agreement), согласование (coordination), соглашатель (appeaser), согласно (accordingly), etc.
I am struck by the similarity between Czech hlas and Welsh llais (voice). There is no analogous construct that I know of based on llais but there is a similar construct based on the (perhaps related) noun llafar (speech), albeit not with quite the same meaning:
cyflafareddu = ‘to arbitrate’
cyf- being a prefix roughly equivalent to Romance con- (=’with’)
The Latvian word for ‘to agree’ is piekrist (pie- = ‘by’; krist = ‘to fall’). The Latvian word for voice, incidentally, is balss, presumably related to the Slavic forms hlas and глас. http://www.etymonline.com does not suggest any connection between these words and those of Romance derivation (voice, voix, vocem etc.).
German has “zustimmen”, which is constructed the same way (die Stimme = voice), as well as “abstimmen” (to decide by vote, to co-ordinate), “übereinstimmen” (to agree, to correspond to), “einstimmig” (unanimous), and probably some other words I can’t think of right now.