Army without backing for decoration (6)
I believe the answer is:
'decoration' is the definition.
(tassel is a kind of decoration)
'army without backing' is the wordplay.
'army' becomes 'ta' (abbreviation for Territorial Army).
'without' becomes 'less'.
'backing' is a reversal indicator.
'less' written backwards gives 'ssel'.
'for' acts as a link.
(Other definitions for tassel that I've seen before include "Hanging bunch of cords" , "Ornamental tuft of threads" , "Decorative hanging tuft" , "Hanger-on perhaps" , "Decorative tuft of threads" .)