Eight things tomcats eat regularly (5)
I believe the answer is:
octet
'eight' is the definition.
(synonyms)
'tomcats eat regularly' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'tomcats'+'eat'='tomcatseat'
The alternating letters of 'tomcatseat' are 'OCTET'.
'things' is the link.
(Other definitions for octet that I've seen before include "Musical work for eight" , "music group" , "Musical composition for eight performers" , "Chamber ensemble, a Mendelssohn favourite" , "A group of eight instruments or voices" .)