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- .
[ ad, ad- (prep. and prefix) to, toward, at, about; c. AT 1 ]