Dramatic partner is oddly cross with sailor (6)
I believe the answer is:
costar
'dramatic partner' is the definition.
I know nothing about this answer so I can't tell whether this works.
'oddly cross with sailor' is the wordplay.
'oddly' means one should take alternating letters (letters in the odd-numbered positions are used).
'with' is a charade indicator (letters next to each other).
'sailor' becomes 'tar' (tar can mean a sailor).
The alternating letters of 'cross' are 'cos'.
'cos'+'tar'='COSTAR'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for costar that I've seen before include "top the bill with another" , "One of the top players" , "one of a pair?" .)