Lied terribly after mountain pass crash (7)
I believe the answer is:
collide
'crash' is the definition.
(I've seen this before)
'lied terribly after mountain pass' is the wordplay.
'terribly' indicates anagramming the letters.
'after' means one lot of letters go next to another.
'mountain pass' becomes 'col' (col is a kind of mountain pass).
'lied' anagrammed gives 'lide'.
'lide' put after 'col' is 'COLLIDE'.
(Other definitions for collide that I've seen before include "Smash together" , "Dash together; clash" , "Run into" , "Hit" , "Crash together" .)