Meaning of know-not-what in English:

know-not-what

Pronunciation /ˌnəʊnɒtˈwɒt/

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.