once
UK[wʌns]US[wʌns]
adv
On one occasion only; one time.
adv
At some time in the past; formerly.
conj
As soon as; when.
Etymology
The word 'once' originates from the Old English 'ānes', the genitive singular form of 'ān', meaning 'one'. This genitive construction, literally translating to 'of one', was used adverbially to signify 'one time' or 'on one occasion'. Over time, the Middle English form 'ones' evolved, and the modern spelling 'once' became standardized, influenced by other adverbs ending in '-ce' like 'hence' and 'thence'. Its core meaning has remained remarkably stable, expanding from a simple temporal adverb to also function as a conjunction introducing a conditional temporal clause.
Analysis
The word is a simplex form derived from the Old English phrase 'ānes', the genitive case of 'ān' (one), used to form an adverbial expression meaning 'one time'.
Examples
I've only been to Paris once.
This house was once the village school.
Once you understand the rules, the game becomes much easier.