Loyalty for one entering partnership (10)
I believe the answer is:
allegiance
'loyalty' is the definition.
(allegiance is a kind of loyalty)
'for one entering partnership' is the wordplay.
'for one' becomes 'eg' (both can mean 'for example').
'entering' indicates putting letters inside.
'partnership' becomes 'alliance' (I've seen this before).
'eg' inserted inside 'alliance' is 'ALLEGIANCE'.
(Other definitions for allegiance that I've seen before include "commitment to a cause" , "duty" , "Loyalty to a group or cause" , "Loyalty (to a superior)" , "Fidelity" .)