Climbing frame initially lacking snake (5)
I believe the answer is:
adder
'snake' is the definition.
(type of snake)
'climbing frame initially lacking' is the wordplay.
'climbing frame' becomes 'ladder' (I've seen this before).
'initially lacking' means to remove the first letter.
'ladder' with its initial letter taken away is 'ADDER'.
(Other definitions for adder that I've seen before include "Venemous snake" , "British snake; summer" , "exhibit in the reptile house" , "on country walks?" , "venomous creature" .)