Material authority I had (5)
I believe the answer is:
plaid
'material' is the definition.
(plaid is a kind of material)
'authority i had' is the wordplay.
'authority' becomes 'pla' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'i had' becomes 'i'd' (contraction).
'pla'+'id'='PLAID'
Can you help me to learn more?
(Other definitions for plaid that I've seen before include "Cloth with a criss-cross design" , "Scotsman's cloth" , "material" , "Tartan-pattern cloth" , "Tartan twilled cloth" .)