Merriam-Webster Collegiate Dictionary - ad-

 or ac- or af- or ag- or al- or ap- or as- or at-  prefix  Etymology: Middle English, from Anglo-French & Latin; Anglo-French, from Latin, from ad — more at at  1. to ; toward — usually ac- before c, k, or q acculturation and af- before f affluent and ag- before g aggradation and al- before l alliteration and ap- before p apportion and as- before s assuasive and at- before t attune and ~ before other sounds but sometimes ~ even before one of the listed consonants adsorb  2. near ; adjacent to — in this sense always in the form ~ adrenal