In the meantime I'm after it (5)
I believe the answer is:
inter
'i'm after it' is the definition.
I can't tell whether this definition defines the answer.
'in the meantime' is the wordplay.
'the meantime' becomes 'ter' (I can't justify this - if you can you should believe this answer much more).
'in'+'ter'='INTER'
Can you help me to learn more?
(Other definitions for inter that I've seen before include "Place into grave, tomb" , "Football Club at home in San Siro" , "Put under the earth" , "somewhere between ..." , "team from Italy" .)