There’s very little we have a key for (3)
I believe the answer is:
wee
'a key for' is the definition.
The definition suggests a singular noun which matches the answer.
'there's very little we have' is the wordplay.
'there's' means one lot of letters go next to another.
'very little' says to take the initial letters.
'have' becomes 'ee' (I am not sure about this - if you are sure you should believe this answer much more).
The first letter of 'we' is 'w'.
'w' put next to 'ee' is 'WEE'.
Can you help me to learn more?
(Other definitions for wee that I've seen before include "Tiny (Scot)" , "Little or tiny in Scotland" , "Little (Scottish)" , "Slash" , "squeal" .)