late 13c., auys "opinion," from Old French avis "opinion, view, judgment, idea" (13c.), from phrase ço m'est à vis "it seems to me," or from Vulgar Latin *mi est visum "in my view," ultimately from Latin visum, neuter past participle of videre "to see" (from PIE root *weid- "to see").
Meaning "opinion offered as worthy to be followed, counsel" is from late 14c. The unetymological -d- (on model of Latin words in ad-) was inserted occasionally in French by scribes 14c.-16c. and was made regular in English 15c. by Caxton. Substitution of -c- for -s- is 18c., to preserve the breath sound and to distinguish from advise.