Relative who men trail nervously? (6-2-3)
I believe the answer is:
mother-in-law
'relative' is the definition.
(mother-in-law is a kind of relative)
'who men trail nervously?' is the wordplay.
'nervously?' indicates anagramming the letters (I've seen 'nervously' mean this).
'who'+'men'+'trail'='whomentrail'
'whomentrail' with letters rearranged gives 'MOTHER-IN-LAW'.
(Other definitions for mother-in-law that I've seen before include "Relative by marriage" , "Relative - woman Hitler (anag)" .)