what's-her-name

• what'shername, whatshername, what's-'er-name, what's'ername, what'sername, whats'ername, whatsername, whatsename, whasername
• who's-her-name, who'shername, whoshername, whosername
• what's-her-butt, what'sherbutt, whatsherbutt (Canada, US, uncommon)

Univerbation of what's +‎ her +‎ name.

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

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

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

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

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

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

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

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