Informal neckwear injured people (10)
I believe the answer is:
casualties
'injured people' is the definition.
(I've seen this before)
'informal neckwear' is the wordplay.
'informal' becomes 'casual' (similar in meaning).
'neckwear' becomes 'ties' (I've seen this in another clue).
'casual'+'ties'='CASUALTIES'
(Other definitions for casualties that I've seen before include "Victims" , "Injured people" .)