what's-his-name

• what'shisname, whatshisname, what's-'is-name, what's'isname, what'sisname, whats'isname, whatsisname, whatsename, whasisname
• who's-his-name, who'shisname, whoshisname, whosisname
• what's-his-butt, what'shisbutt, whatshisbutt (Canada, US, uncommon)

Univerbation of what's +‎ his +‎ name.

what's-his-name (plural what's-their-names)

1. (informal, chiefly in the singular) A man whose identity is unknown or forgotten (especially when better-known to the listener).

   Near-synonyms: what's-his-face (what's-her-face, what's-their-face); whatchamacallhim (whatchamacallher); you-know-who; so-and-so; see also Thesaurus:what's-their-name

   Coordinate terms: what's-her-name, what's-their-name

   • 1842, Robert Browning, Waring:

     I left his arm that night myself / For what's-his-name's, the new prose-poet / Who wrote the book there, on the shelf

   • 1885, W[illiam] S[chwenck] Gilbert; Arthur Sullivan, composer, […] The Mikado; or, The Town of Titipu, London: Chappel & Co., […], →OCLC:

     And 'St—'st—'st and What's-his-name, and also You-know-who— / The task of filling up the blanks I'd rather leave to you.

what's-his-name (plural what's-his-names)

1. (informal, derogatory, chiefly in the plural) A passing (male) acquaintance of no importance or relevance.

   Coordinate terms: what's-her-name, what's-their-name

• Note that the plural is what's-their-names for the pronoun and what's-his-names for the noun.
• Reduced forms such as whatsename and whasisname are only used for the pronoun, and typically only in speech.