Bird sailor associated with sunrise, mostly (7)
I believe the answer is:
jackdaw
'bird' is the definition.
(jackdaw is a kind of bird)
'sailor associated with sunrise mostly' is the wordplay.
'sailor' becomes 'jack' (I've seen this before).
'associated with' says to put letters next to each other.
'sunrise' becomes 'dawn' ('dawn' can be a synonym of 'sunrise').
'mostly' means to remove the last letter.
'dawn' with its last letter taken off is 'daw'.
'jack'+'daw'='JACKDAW'
(Other definitions for jackdaw that I've seen before include "Black bird" , "Crows relative" , "Thieving bird" , "Grey-headed crow" , "Member of crow family noted for thieving" .)