Severe strain unsettled man (10)
I believe the answer is:
astringent
'severe' is the definition.
(I've seen this before)
'strain unsettled man' is the wordplay.
'unsettled' is an anagram indicator.
'man' becomes 'gent' (gent is a kind of man**).
'strain' anagrammed gives 'astrin'.
'astrin'+'gent'='ASTRINGENT'
(Other definitions for astringent that I've seen before include "Severe - checking the flow of blood" , "Harsh" , "Styptic" , "biting" , "Lotion" .)