Getting only four in a test is unimportant (7)
I believe the answer is:
trivial
'unimportant' is the definition.
(similar in meaning)
'getting only four in a test' is the wordplay.
'getting' means one lot of letters goes inside another.
'only four in' becomes 'vi' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a test' becomes 'trial' ('trial' can be a synonym of 'test').
'vi' placed into 'trial' is 'TRIVIAL'.
'is' is the link.
Can you help me to learn more?
(Other definitions for trivial that I've seen before include "Of little consequence" , "Very easy" , "Petty, piffling" , "Quite unimportant and paltry" , "Inconsequential, too minor to be bothered about" .)