The word element ad- is not an active prefix in English; that is, it is not used to create new words. It comes from the Latin preposition ad, meaning “to, toward, on top of.” In Latin, this preposition became a prefix, and when it was followed by c, f, g, l, n, r, s, or t, it became ac, af, ag, al, an, ar, as, or at, respectively. Thus Latin ad- is easy to see in English words such as adhere, admit, and adverse, but it is not so obvious in words such as affix, apply, and attend.
