Group of creatures that is restricted by singular muscles (7)
I believe the answer is:
species
'group of creatures' is the definition.
'species' can be an answer for 'group' (eg group of animals). I am unsure of the 'of creatures' bit.
'that is restricted by singular muscles' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'restricted by' means one lot of letters goes inside another (inserted letters are restricted or trapped).
'singular' becomes 's' (abbreviation in grammar).
'muscles' becomes 'pecs' (short for pectoral muscles).
's'+'pecs'='specs'
'ie' going into 'specs' is 'SPECIES'.
Can you help me to learn more?
(Other definitions for species that I've seen before include "Groups of related plants or animals" , "Taxonomic group whose members can interbreed" , "Variety, taxonomic group" , "Taxonomic grouping" , "Sort, type" .)