pin somebody/something ↔ down phrasal verb ( see also ↑ pin )
1 . to make someone give clear details or make a definite decision about something
pin somebody/something ↔ down to
Did you manage to pin him down to a definite date?
He’s impossible to pin down.
2 . to understand something clearly or be able to describe it exactly
hard/difficult to pin down
The flavour was hard to pin down.
3 . if soldiers etc involved in fighting are pinned down, they cannot move from their position because someone is shooting at them:
The rebels have been pinned down in a camp to the south of the river.