Restrictive of lithium, metal used in aircraft (8)
I believe the answer is:
limiting
'restrictive' is the definition.
('limiting' can be similar in meaning to 'restrictive')
'lithium metal used in aircraft' is the wordplay.
'lithium' becomes 'li' ('Li' can be a synonym of 'lithium').
'metal' becomes 'tin' (tin is a kind of metal**).
'used in' means one lot of letters goes inside another.
'aircraft' becomes 'mig' (I have seen 'Russian aircraft ' mean 'mig' so perhaps 'aircraft' could also mean 'mig').
'tin' put inside 'mig' is 'miting'.
'li'+'miting'='LIMITING'
'of' is the link.
(Other definitions for limiting that I've seen before include "Bounding" , "cutting back" , "Restricting scope or freedom" , "Checking" .)