A writer mostly associated with a group of stars (6)
I believe the answer is:
aquila
'group of stars' is the definition.
(I've seen this before)
'a writer mostly associated' is the wordplay.
'writer' becomes 'quill' (item which writes).
'mostly' means to remove the last letter (most but not all of the word).
'associated' becomes 'a' (this might be a standard abbreviation which I don't know about).
'quill' with its final letter taken away is 'quil'.
'a'+'quil'+'a'='AQUILA'
'with a' acts as a link.
Can you help me to learn more?
(Other definitions for aquila that I've seen before include "Italian city" , "Constellation, the Eagle" , "group of stars" , "Altair's constellation" , "Stars gathered together" .)