Meaning of AD- in English
[ad-] or ac- or af- or ag- or al- or ap- or as- or at- prefix [ME, fr. MF, OF & L; MF, fr. OF, fr. L, fr. ad--more at at] 1: to: toward--usu. 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 ad- before other sounds but sometimes ad- even before one of the listed consonants "adsorb"
2: near: adjacent to--in this sense always in the form ad- "adrenal"
Merriam-Webster English vocab. Английский словарь Merriam Webster. 2012