Tuna chopped by son for relatives (5)
I believe the answer is:
aunts
'relatives' is the definition.
(aunt is a kind of relative)
'tuna chopped by son' is the wordplay.
'chopped' indicates anagramming the letters (letters chopped or smashed up).
'by' says to put letters next to each other.
'son' becomes 's' (genealogical abbreviation for son).
'tuna' is an anagram of 'aunt'.
'aunt'+'s'='AUNTS'
'for' acts as a link.
(Other definitions for aunts that I've seen before include "Female relatives, usually older" , "Elderly female relations" , "Relatives get an odd US tan" , "relatively speaking" , "Relatives get a peculiar US tan" .)