Stick 150 in Greek capital (5)
I believe the answer is:
cling
'stick' is the definition.
('cling' can be a synonym of 'stick')
'150 in greek capital' is the wordplay.
'150' becomes 'cl' (roman numerals).
'capital' says to take the initial letters.
The initial letter of 'greek' is 'g'.
'cl'+'in'+'g'='CLING'
(Other definitions for cling that I've seen before include "Keep hold" , "Hold, cleave" , "Adhere to - ring" , "fast" , "have emotional attachment?" .)