Back is an adverb, noun, adjective or verb.
Back can mean ‘returning to an earlier starting point or situation’ or ‘moving to a point further away’ or ‘replying to something’. Back also means ‘at the rear of’ or ‘the part of a person or thing that is opposite the front’.
Back as an adverb
Olga’s not looking forward to going back to school in September.
[taking a photograph]
Don’t move too far back or you’ll fall in the swimming pool.
Sorry, I’m just finishing a meeting. Can I ring you back in ten minutes?
Back as a noun
There’s a new restaurant at the back of our office building.
Will Hoskins is unlikely to play as he hurt his back badly playing in the Rugby World Cup semi-final and is still receiving treatment.
Back as an adjective
The reporters were chasing her and, in order to avoid the cameras, she had to use the back door of the theatre.
Unfortunately she’s spilt coffee over the back seat of the car.
Back as a verb
[talking about a pet dog]
He’s got a lovely temperament but he may panic and bite you if you back him into a corner.
Did you know that during his driving test he backed his car into a bicycle?