Struggle to get iron in sheet (5)
I believe the answer is:
wafer
'sheet' is the definition.
(thesaurus)
'struggle to get iron' is the wordplay.
'struggle' becomes 'war' (warring is a kind of struggling).
'to get' means one lot of letters goes inside another.
'iron' becomes 'fe' (Fe is the chemical symbol for iron).
'war' going around 'fe' is 'WAFER'.
'in' is the link.
(Other definitions for wafer that I've seen before include "thin stuff" , "Ice-cream biscuit" , "Host's" , "Ice cream's biscuit" , "Disc of bread" .)