A second husband’s remains (3)
I believe the answer is:
ash
'remains' is the definition.
(remains of a fire)
'a second husband's' is the wordplay.
'second' becomes 's' (common abbreviation).
'husband' becomes 'h'.
'a'+'s'+'h'='ASH'
(Other definitions for ash that I've seen before include "Hard pale wood" , "... for this maybe" , "One [TYPE OF TREE]" , "Dusty residue of a fire" , "Silvery grey" .)