As an adverb its general meaning is:
- away, as in ‘If you don’t need me any more I’ll be off’ ;or
- not on or not connected to something, as in ‘She tried to push the dog off but it kept jumping up’.
As a preposition, it can mean:
- close to something, as in ‘The restaurant is just off the main road’ or ‘Two miles off the coast we ran into a terrible storm’.
- you are no longer eating, using or doing something, as in ‘I’ve been off alcohol now for three weeks’ or ‘I’m off sweet things at the moment’.
As an adjective,Off can also mean:
- that an event is no longer going to take place as planned, as in ‘Tonight’s match is off due to a waterlogged pitch’, or
- that something is no longer good, as in ‘I wouldn’t eat that meat if I were you. I think it’s off’.
- In the context of a restaurant, it can also mean that something is not available, as in ‘I’m sorry, sir, but the roast lamb is off.
- If used to describe behavior, off is normally preceded by the phrase a bit and can mean strange or unusual, or even unacceptable and impolite, as in ‘Something about the way he talked was a bit off’ or ‘I thought the way he interrupted you was a bit off’.
- Off is also used with well and badly. If you are well off, you are rich but if you are badly off, you are poor.
Finally, as a noun, the off means:
- the beginning of something such as a sporting event or a party, as in ‘We were all there waiting for the off when the lights went out’.
Thanks to Tim Bowen at onestopenglish.com