Hold on both sides of Greek ship (4)
I believe the answer is:
grip
'hold on both sides' is the definition.
'grip' can be an answer for 'hold' ('grip' can be a synonym of 'hold'). I'm not certain of the 'on both sides' bit.
'greek ship' is the wordplay.
'greek' becomes 'gr'.
'ship' becomes 'ip' (I can't justify this - if you can you should give a lot more credence to this answer).
'gr'+'ip'='GRIP'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for grip that I've seen before include "Grasp tightly" , "Grasp securely" , "Stagehand" , "member of camera crew" , "Catch" .)