Motion or direction to; reduction or change into; addition, increase, or intensification.
[Latin ad, to]
Many loanwords from Latin containing this prefix took on a modified or figurative sense in Latin and they retain it in English. For example, adore is from Latin orare, to speak or pray, via a late Latin form adorare, to worship; addict originally meant to be assigned by decree to do something (Latin dicere, to say), but later shifted sense in English to refer to an attachment to one's own inclinations. Other examples of similar kind are adolescent, adjacent, advocate, and adequate.
In Latin the prefix changes according to the initial letter of the word to which it is attached—it can appear as a- (before sc and sp), ac- (before c and q), and as af-, ag-, al-, an-, ap- , ar-, as-, and at-, in each case before stems beginning with the second letter of the form. A few examples of a large group are ascribe (Latin scribere, to write), acquire (Latin quaerere, to seek), affluent (Latin fluere, to flow), agglomerate (Latin glomus, a ball), allocate (Latin locare, location), annihilate (Latin nihil, nothing), appetite (Latin petere, to seek), arrest (Latin restare, remain or stop), assail (Latin salire, to leap), and attempt (Latin temptare, to tempt).