A duck one possibly links with waterproof cover (7)
I believe the answer is:
oilskin
'waterproof cover' is the definition.
'oilskin' can be an answer for 'cover' (I have seen 'protective cover' mean 'oilskin' so perhaps 'cover' could also mean 'oilskin'). I'm not certain of the 'waterproof' bit.
'a duck one possibly links' is the wordplay.
'a duck' becomes 'o' (resembles zero - 'duck' in cricket).
'one' becomes 'i' (Roman numeral).
'possibly' is an anagram indicator.
'links' is an anagram of 'lskin'.
'o'+'i'+'lskin'='OILSKIN'
'with' acts as a link.
Can you help me to learn more?
(Other definitions for oilskin that I've seen before include "Protective coat" , "Waterproof cloth for rain-gear" , "Heavy waterproofed cloth" , "protection for Ainslie?" , "Heavy-duty waterproof" .)