Rely on foul saving time for wing (7)
I believe the answer is:
elytron
'wing' is the definition.
(wing case of a beetle)
'rely on foul saving time' is the wordplay.
'foul' indicates an anagram.
'saving' indicates putting letters inside.
'time' becomes 't' (abbreviation).
'rely'+'on'='relyon'
'relyon' with letters rearranged gives 'elyron'.
'elyron' enclosing 't' is 'ELYTRON'.
'for' is the link.
(Other definitions for elytron that I've seen before include "bit of a bug?" , "beetle wing" .)