Little devil is impolite at first (3)
I believe the answer is:
imp
'little devil' is the definition.
(an imp is a little demon)
'impolite at first' is the wordplay.
'impolite' becomes 'mp' (I can't justify this - if you can you should believe this answer much more).
'at' says to put letters next to each other (I've seen this in other clues).
'first' becomes 'i' (I in Roman numerals eg Elizabeth I).
'mp' after 'i' is 'IMP'.
'is' is the link.
Can you help me to learn more?
(Other definitions for imp that I've seen before include "Pixie" , "Rascal" , "Small demon" , "Goblin" , "Small mischievous spirit" .)