From Latin 'unicus' (only one of its kind), from 'unus' (one) — a Latin cousin of English 'one.'
Being the only one of its kind; unlike anything else; particularly remarkable or unusual.
From French unique (sole, only, single), from Latin ūnicus (one only, sole, singular, without equal), from ūnus (one), from PIE *óynos (one, single). The word literally means one-of-a-kind — not merely rare but ontologically solitary, without duplicate or equal. Latin ūnicus was a strong word: Cicero used it of utterly singular phenomena. English borrowed it in the early 17th century in this absolute sense, but through the 18th–19th centuries unique gradually weakened under the influence of French
Prescriptive grammarians have long insisted that 'unique' is an absolute — something either is unique or is not, so 'very unique' or 'somewhat unique' should be impossible. But language rarely respects logical absolutes: the colloquial sense of 'unique' meaning 'remarkable' rather than 'sole' has been standard in spoken English for over a century.