Definition of ad- in English:

ad-

prefix

  • 1Denoting motion or direction to.

    ‘advance’
    • ‘adduce’
    1. 1.1Reduction or change into.
      ‘adapt’
      • ‘adulterate’
    2. 1.2Addition, increase, or intensification.
      ‘adjunct’
      • ‘adhere’
      • ‘admixture’

Usage

The prefix ad- is also found assimilated in the following forms: a- before sc, sp (ascend, aspire); ac- before c, q (accede, acquire); af- before f (affiliate); ag- before g (aggregate); al- before l (allude); an- before n (annex); ap- before p (appall); ar- before r (arrest); as- before s (assume); at- before t (attend)

Origin

From Latin ad ‘to’; in the 16th century the use of ad- and its variants was extended to replace a- from a different origin such as Latin ab- (e.g. advance, from French avancer based on late Latin abante ‘in front’).