Is a collector, one understands (7)
I believe the answer is:
gathers
'understands' is the definition.
('gather' can be a synonym of 'understand')
'is a collector one' is the wordplay.
I cannot really understand how this works, but
'a' is within the answer.
'one' could be 'the' (both can introduce a definite example of something) and 'the' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for gathers that I've seen before include "Collects in one place" , "Draws together" , "Assembles" , "The rags (anag.)" , "Part of dress" .)