Definition of know-not-what in English:

know-not-what

noun

rare
  • An indescribable thing; a ‘whatchamacallit’. Also with the: that which is indescribable or unknown.

Origin

Mid 17th century; earliest use found in John Suckling (d. ?1641), poet. From know + not + what [adjective¹, adverb].

Pronunciation

know-not-what

/ˌnəʊnɒtˈwɒt/