Meaning of “pin sth down” - Learner’s Dictionary

pin sth down

phrasal verb with pin uk us /pɪn/ verb [ T ] (present participle pinning, past tense and past participle pinned)

to discover exact details about something:

Investigators are trying to pin down the cause of the fire.

(Definition of “pin sth down” from the Cambridge Learner’s Dictionary © Cambridge University Press)