1943—a devilish insect symbolising reckless extravagance and waste—introduced by the National Savings Committee in a government publicity campaign promoting economy—hence: one who is profligate with money or resources
1907—whether one likes it or not; haphazardly—a humorous variant of ‘willy-nilly’, after the personal name ‘William’ (‘William’ being familiarly shortened to ‘Willy’)
USA, 1927—denotes male vigour, especially sexual—with wordplay on ‘penis’—interestingly, via an alteration of the Latin diminutive ‘pēnĭcillus’, denoting literally a little tail, hence a painter’s brush or pencil, ‘pencil’ is derived from Latin ‘pēnis’, denoting literally a tail, hence the penis
USA (New England), 1868—alternately sunny and cloudy conditions usually indicate rain—the adjective ‘shet’ is a variant of ‘shut’—it was perhaps in order to provide a rhyme for the adjective ‘wet’ that the variant ‘shet’ was chosen in the proverb
UK, 1925—the verb ‘Adam and Eve’ is rhyming slang for ‘to believe’—there is no truncation, contrary to the usual rhyming-slang formation (cf. ‘scooby’, rhyming slang for ‘clue’, which is short for ‘Scooby Doo’)
USA, 1901—wonderfully stylish, elegant or fashionable—a blend of ‘swell’ and ‘elegant’—popularised by its use in the song Well, Did You Evah!, interpreted by Bing Crosby and Frank Sinatra in the 1956 film High Society
1945—a woman from Liverpool, a city and seaport in north-western England—from the noun ‘Scouser’, denoting a person from Liverpool, and the suffix ‘-ette’, used to form nouns denoting female gender
UK, 1933—a jump made with a parachute—hence also the verbal noun ‘brolly-hopping’ and the verb ‘brolly-hop’—‘brolly’ (university slang, late 19th century): a clipped and altered form of ‘umbrella’
On the pattern of phrases such as ‘nom de guerre’, ‘nom de théâtre’ and ‘nom de plume’, ‘nom de —’ is used, often humorously, to form phrases denoting a pseudonym, an alternative name.