Saint boarding moving train to get cover (9)
I believe the answer is:
tarpaulin
'cover' is the definition.
(I know that tarpaulin is a type of cover)
'saint boarding moving train' is the wordplay.
'saint' becomes 'Paul' (St Paul).
'boarding' is an insertion indicator.
'moving' is an anagram indicator (letters are moved around).
'train' is an anagram of 'tarin'.
'paul' going into 'tarin' is 'TARPAULIN'.
'to get' acts as a link.
(Other definitions for tarpaulin that I've seen before include "protective cover" , "It provides protection" , "oilskin hat" , "waterproof material" , "Heavy waterproof cover" .)