What part of speech is “until”

the preposition 'until' can be used when you want to indicate that something did not occur before a certain point in time.

1. I will be working until my shift ends at midnight.

2. I waited until the sun set before going home.

3. I cannot attend your event until next week.

it is important to remember that 'until' is used exclusively when referring to a point in time in the future. If you need to refer to a point in time in the past, you should use the word 'by' instead. Additionally, it is often used with the auxiliary verb 'will' to express the idea that something will continue until a certain point in time.