Slip on mountain pass and fall down (8)
I believe the answer is:
collapse
'fall down' is the definition.
(I've seen this before)
'slip on mountain pass' is the wordplay.
'slip' becomes 'lapse' (lapsing is a kind of slipping).
'on' means one lot of letters go next to another.
'mountain pass' becomes 'col' (col is a kind of mountain pass).
'lapse' after 'col' is 'COLLAPSE'.
'and' is the link.
(Other definitions for collapse that I've seen before include "Fall down unconscious" , "Sudden breakdown" , "Fall down as from weakness" , "Crumble" , "Suddenly fall down or give way" .)