nail down

Establish conclusively, as in The reporter nailed down the story by checking all the facts. This metaphoric expression alludes to fixing or fastening something down with nails. [c. 1600]

The verb has 3 meanings:

Meaning #1: succeed in obtaining a position
  Synonyms: nail, peg

Meaning #2: define clearly
  Synonyms: pin down, peg down, narrow down, narrow, specify

Meaning #3: make final; put the last touches on; put into final form
  Synonyms: finalize, finalise, settle