From Longman Dictionary of Contemporary Englishpin somebody/something ↔ down phrasal verb1 FIND OUTto make someone give clear details or make a definite decision about something to Did you manage to pin him down to a definite date? He’s impossible to pin down.2 UNDERSTANDto understand something clearly or be able to describe it exactlyhard/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. → pin→ See Verb table
Examples from the Corpus
pin to• As regards yeomen the statistics serve chiefly to emphasise the difficulty of pinning them down to a precise definition.• By that I do not mean than one can not pin them down to set feeding patterns on specific waters.hard/difficult to pin down• An explanation from Lipsey for his withdrawal Friday has been hard to pin down.• Since flavour is an emotive as well as a factual quality, it is hard to pin down.• It was little wonder that, during this time, Gergiev proved difficult to pin down for a promised meeting.• The precise moment when it was first questioned is hard to pin down for sure.• It is hard to pin down something as elusive as a good school climate.• Although we will clarify it in the course of this study, multimedia is hard to pin down to a rigid definition.• On the other hand, he was extremely difficult to pin down to any conclusion. 