Definition of for- in US English:

for-

prefix

  • 1Denoting prohibition.

    ‘forbid’
  • 2Denoting abstention, neglect, or renunciation.

    ‘forgive’
    ‘forget’
    ‘forgo’
  • 3Denoting extremity of negative state expressed.

    ‘forlorn’
    ‘forsake’

Origin

Old English.