Chuck starts writing for openings (6)
I believe the answer is:
chasms
'for openings' is the definition.
(chasm is a kind of opening)
'chuck starts writing' is the wordplay.
'chuck starts' becomes 'chas' (I can't justify this - if you can you should believe this answer much more).
'writing' becomes 'ms' (abbreviation for manuscript).
'chas'+'ms'='CHASMS'
Can you help me to learn more?
(Other definitions for chasms that I've seen before include "Deep fissures in the earth" , "Deep fissure in the earth" , "Deep gorges, crevasses" , "Deep openings in the earth's surface" , "Big gaps" .)