Unnerves the many relatives (6)
I believe the answer is:
daunts
'unnerves' is the definition.
(I've seen this in another clue)
'many relatives' is the wordplay.
'many' becomes 'D' (Roman numeral for 500).
'relatives' becomes 'aunts' (aunt is a kind of relative).
'd'+'aunts'='DAUNTS'
'the' acts as a link.
(Other definitions for daunts that I've seen before include "Cows" , "Frightens or discourages" , "Makes afraid or discouraged" , "intimidates" .)