Ten labouring on a chain — harsh (10)
I believe the answer is:
astringent
'harsh' is the definition.
(harsh can mean astringent or severe)
'ten labouring on a chain' is the wordplay.
'labouring' indicates an anagram (letters worked or laboured into a new form).
'on' says to put letters next to each other.
'chain' becomes 'string' (synonyms).
'ten' anagrammed gives 'ent'.
'a'+'string'='astring'
'ent' after 'astring' is 'ASTRINGENT'.
(Other definitions for astringent that I've seen before include "biting" , "Severe - checking the flow of blood" , "Sharp or severe in manner" , "Caustic" , "Scathing" .)