Living things in grass? Mom almost in a frenzy (9)
I believe the answer is:
organisms
'living things' is the definition.
('organism' can be a synonym of 'living thing')
'grass? mom almost in a frenzy' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'a frenzy' is an anagram indicator.
'grass'+'mom'='grassmom'
'grassmom' with its final letter removed is 'grassmo'.
'grassmo'+'in'='grassmoin'
'grassmoin' is an anagram of 'ORGANISMS'.
'in' is the link.
(Other definitions for organisms that I've seen before include "So margins, strangely, could be living things" , "Living systems of Mrs Saigon" , "Strange living structures of Mrs Saigon" .)