Crossing round head of jungle's inlet (5)
I believe the answer is:
fjord
'inlet' is the definition.
(fjord is a kind of inlet)
'crossing round head of jungle's' is the wordplay.
'crossing' becomes 'ford' (ford is a kind of crossing).
'round' means one lot of letters goes inside another.
'head of' suggests taking the first letters.
The first letter of 'jungles' is 'j'.
'ford' placed around 'j' is 'FJORD'.
(Other definitions for fjord that I've seen before include "Long narrow inlet" , "Northern location?" , "Rocky inlet" , "Norwegian inlet (J, not I)" , "Rock-bound inlet" .)