Dad intermittently uses way through mountains (4)
I believe the answer is:
pass
'way through mountains' is the definition.
(I've seen this before)
'dad intermittently uses' is the wordplay.
'dad' becomes 'pa' (both can mean one's father).
'intermittently' indicates alternate letters.
The alternating letters of 'uses' are 'ss'.
'pa'+'ss'='PASS'
(Other definitions for pass that I've seen before include "exam grade ..." , "Go by; mountain route" , "Succeed; overtake" , "Hand over < identity card" , "while away" .)