Heavy work poorly received by soldiers (7)
I believe the answer is:
gorilla
'heavy' is the definition.
(I've seen this before)
'work poorly received by soldiers' is the wordplay.
'work' becomes 'go' (synonyms).
'poorly' becomes 'ill' (similar in meaning).
'received by' means one lot of letters goes inside another.
'soldiers' becomes 'RA' (abbreviation for Royal Artillery).
'ill' put within 'ra' is 'rilla'.
'go'+'rilla'='GORILLA'
(Other definitions for gorilla that I've seen before include "Large primate" , "Chest-beating primate" , "Primate - sturdily-built aggressive man" , "big mammal" , "Aggressive-looking type" .)