Avail

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Middle English: from obsolete vail ‘be of use or value’ (apparently on the pattern of pairs such as amount, mount ), from Old French valoir, from Latin valere ‘be strong, be of value’.

wiktionary

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From Middle English availen(“to be of use”), from Old French a(“to”) + vail (from valoir(“to be worth”)).

etymonline

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avail (v.)

c. 1300, availen, "to help (someone), assist; benefit, be profitable to; be for the advantage of; have force or efficacy, serve for a purpose," apparently an Anglo-French compound of Old French a- "to" (see ad-) + vaill-, present stem of valoir "be worth," from Latin valere "be strong, be worth" (from PIE root *wal- "to be strong"). Related: Availed; availing. As a noun, from c. 1400.