Until

Until is an English word used to indicate that something continues up to a specified time or event. It functions primarily as a preposition and as a conjunction, introducing a time phrase or a dependent clause: "Stay until noon," "We waited until the rain stopped." When used with a negative sentence, "not until" can emphasize the delay: "The store did not open until 9 a.m."

Etymology and spelling variants: Until derives from Old English untill, a compound form related to til (to, toward). The modern spelling until became standard in Modern English; till is a common variant, and ’til is an informal contraction. Note that till can also mean a cash register in retail, which is unrelated to time.

Usage notes: Until is used with time expressions and events: "We can stay until the sun sets," or "We will not leave until tomorrow." It can be followed by a noun phrase (until 5 PM) or by a clause (until you arrive). Not until is often used to create emphasis: "Not until yesterday did I realize." Phrases such as until now or until then anchor a narrative.

Overall, until is standard in American and British English. In formal writing, until is preferred over shorter contractions; till or ’til appear more often in informal contexts. Be aware that till also exists as a noun meaning a cash register, a usage unrelated to the temporal sense.