sine-qua-nons, n. — Green’s Dictionary of Slang

sine-qua-nons n.

[euph. use of Lat. sine qua non, lit. without which not, i.e. an essential requirement]

trousers.

1928

Exeter & Plymouth Gaz. 7 Mar. 6/6: There was a time when to use the word trousers was almost an indication of a dirty mind. [...] They had been called [...] inexpressibles, indescribables, unwhisperables, mustn’t-mention-ems, sit-upons, sine qua nons, and unutterables.