Small gallery accommodating high-class sculpture (6)
I believe the answer is:
statue
'sculpture' is the definition.
(I know that statue is a type of sculpture)
'small gallery accommodating high-class' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'gallery' becomes 'tate' (Tate Modern, Tate Britain etc).
'accommodating' means one lot of letters goes inside another.
'high class' becomes 'U' (as in U and non-U speech).
'tate' going around 'u' is 'tatue'.
's'+'tatue'='STATUE'
(Other definitions for statue that I've seen before include "Solid representation of the human form" , "A carved image or effigy" , "Sculptured likeness" , "artwork" , "One representing liberty" .)