Open gallery not filled? (7)
I believe the answer is:
artless
'open' is the definition.
(thesaurus)
'gallery not filled?' is the wordplay.
I cannot really see how this works, but
'gallery' could be 'art' (synonyms) and 'art' is located in the answer.
'not' could be 'less' (I've seen this in other clues) and 'less' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for artless that I've seen before include "as an empty gallery" , "Naive - unskilful" , "Free from cunning" , "Simple and natural in manner" , "Natural like slaters" .)