Stick diamonds in a present! (6)
I believe the answer is:
adhere
'stick' is the definition.
('adhere' can be a synonym of 'stick')
'diamonds in a present' is the wordplay.
'diamonds' becomes 'd' (abbreviation in bridge say).
'in' indicates putting letters inside.
'present' becomes 'here' ('here' can be similar in meaning to 'present').
'a'+'here'='ahere'
'd' going within 'ahere' is 'ADHERE'.
(Other definitions for adhere that I've seen before include "Stick like a stamp" , "Stick to - cement" , "paste" , "Stick to as by suction" , "Stick or cleave to" .)