Huge American soldier meets small insect (5)
I believe the answer is:
giant
'huge' is the definition.
(I know that huge can be written as giant)
'american soldier meets small insect' is the wordplay.
'american soldier' becomes 'gi' (informal term for a US soldier).
'meets' says to put letters next to each other.
'small insect' becomes 'ant' (I've seen this before).
'gi'+'ant'='GIANT'
(Other definitions for giant that I've seen before include "Enormous" , "Jumbo" , "Large black and white mammal" , "Ogre" , "Very big chap" .)