1. aff. - Noun
2. aff. - Adjective
(law) Abbreviation of affidavit.
Abbreviation of affair.
(grammar) Abbreviation of affix.
Abbreviation of affiliation or affiliated (with).
(biology) affinis; having affinity with (but not identical to)
(law, archaic) In case citations, Abbreviation of affirmed.
Source: en.wiktionary.org