Put down a deposit (on a nest?) (3)
I believe the answer is:
lay
'put' is the definition.
(as in laying or putting something down)
'down a deposit on a nest?' is the wordplay.
'down a deposit on' becomes 'ly' (I can't explain this - if you can you should give a lot more credence to this answer).
'nest?' indicates putting letters inside (nest' can mean to fit one object into another).
'ly' placed around 'a' is 'LAY'.
Can you help me to learn more?
(Other definitions for lay that I've seen before include "Not a religious" , "gamble" , "Set (table)" , "Not ordained; song" , "located" .)