Tough troops barely mentioned hanger-on (8)
I believe the answer is:
parasite
'hanger-on' is the definition.
(I've seen this in another clue)
'tough troops barely mentioned' is the wordplay.
'tough troops' becomes 'paras' (I can't justify this - if you can you should believe this answer much more).
'barely' says to take the centre (the word is bare of its external letters).
'mentioned' becomes 'cited' ('cite' can be a synonym of 'mention').
The centre of 'cited' is 'ite'.
'paras'+'ite'='PARASITE'
Can you help me to learn more?
(Other definitions for parasite that I've seen before include "mistletoe sprig can be" , "Twenty five dn [LEECH]" , "one who thrives on (or off) another" , "Organism living off another" , "Say mistletoe" .)