'phenylamino' is a compound formation from the combining forms 'phenyl-' and 'amino'. 'Phenyl' is a chemical group name derived in modern chemistry from Neo-Latin/French 'phényle' (ultimately from Greek elements used in chemical naming), and 'amino' comes from 'amine', which is based on 'ammonia' (Latin/Neo-Latin roots).

'phenyl' arose in 19th-century chemical nomenclature as a name for the C6H5– group (from 'phenol' and related roots), while 'amine' was coined in the mid-19th century from 'ammonia'; the combined form 'phenylamino' developed in systematic chemical naming to denote a phenyl-bound amino substituent and appears in modern organic nomenclature.

Initially the parts 'phenyl' and 'amino' named separate chemical entities; over time their concatenation came to denote specifically the substituent C6H5NH– (and adjectival usages) in systematic organic nomenclature.