ad-

a prefix occurring in loanwords from Latin, where it meant "toward" and indicated direction, tendency, or addition: adjoin. Usually assimilated to the following consonant; see a-⁵, ac-, af-, ag-, al-, an- ², ap-¹, ar-, as-, at-.

[ < L ad, ad- (prep. and prefix) to, toward, at, about; c. AT¹]

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