Sound of indifference about small network (4)
I believe the answer is:
mesh
'network' is the definition.
(I know that network can be written as mesh)
'sound of indifference about small' is the wordplay.
'sound of indifference' becomes 'meh' ('meh' is an expression of indifference).
'about' means one lot of letters goes inside another.
'small' becomes 's' (abbreviation - e.g. clothes size).
'meh' going around 's' is 'MESH'.
(Other definitions for mesh that I've seen before include "Engagement" , "Interlaced structure" , "Interconnected configuration" , "Net, snare" , "harmonise" .)