Origin and history of *weid-

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. Early Modern English tended to alternate -ce and -se endings in otherwise confusable noun-verb pairs, using -se for the verb and -ce for the noun: devise/device, peace/appease, practice/practise, license/licence, prophecy/prophesy.

late 13c., avisen "to view, consider" (a sense now obsolete); late 14c., "to give counsel to," from Old French aviser "deliberate, reflect, consider" (13c.), from avis "opinion," 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"). The unetymological -d- is from 16c. Related: Advised; advising.