1. extramarital sex, affair, fooling around

noun (common) (futsuumeishi) intransitive verb noun or participle which takes the aux. verb suru adjectival nouns or quasi-adjectives (keiyodoshi)

2. infidelity, wantonness, unfaithfulness, inconstancy, fickleness, caprice

adjectival nouns or quasi-adjectives (keiyodoshi) intransitive verb noun (common) (futsuumeishi) noun or participle which takes the aux. verb suru