Huge soldier initially greeting worker in charge (8)
I believe the answer is:
gigantic
'huge' is the definition.
(synonyms)
'soldier initially greeting worker in charge' is the wordplay.
'soldier' becomes 'GI' (GI can mean a US soldier).
'initially' suggests taking the first letters.
'worker' becomes 'ant' (worker is a type of ant).
'in charge' becomes 'ic' (abbreviation for 'in charge').
The initial letter of 'greeting' is 'g'.
'gi'+'g'+'ant'+'ic'='GIGANTIC'
(Other definitions for gigantic that I've seen before include "Titanic" , "Great big" , "Huge, enormous" , "monster" , "Thumping" .)