Singular means referring to one only, or remarkably unusual. The singular form, a singular achievement, singularly unhelpful.
The grammatical sense is neutral and technical: one rather than plural. The other sense means so unusual as to stand alone, and it is formal praise. Singularly, the adverb, has drifted to mean simply very, usually before something negative.
1adjectivesingularReferring to one only, or remarkably unusual.
“She was a woman of singular courage who never once gave up.”
singular is a quality.
Latin singularis means alone of its kind, from singulus, single.
Proto-Indo-European
*sem-
Latin
singulāris — alone of its kind
Middle English
singuler
English, today
singular
From Middle English singuler, from Old French -, from Latin singulāris (“alone of its kind”), from Latin singulus (“single”).
Etymology from Wiktionary, CC BY-SA