Passes case forgotten by American soldier containing a spear (7)
I believe the answer is:
assegai
'spear' is the definition.
(assegai is a kind of spear)
'passes case forgotten by american soldier containing a' is the wordplay.
'passes' becomes 'aces' (acing is a kind of passing).
'case' says to hollow out the word (remove centre letters).
'forgotten by' becomes 'se' (I am not sure about this - if you are sure you should believe this answer much more).
'american soldier' becomes 'GI' (informal term for a US soldier).
'containing' means one lot of letters goes inside another.
'aces' with its middle removed is 'as'.
'gi' enclosing 'a' is 'gai'.
'as'+'se'+'gai'='ASSEGAI'
Can you help me to learn more?
(Other definitions for assegai that I've seen before include "Wooden spear of southern Africa" , "A Zulu warrior's spear" , "Sea gas I convert to a Zulu spear" , "African spear" , "something pointed" .)