Impolite and cross, by the sound of it (4)
I believe the answer is:
rude
'impolite' is the definition.
('rude' can be similar in meaning to 'impolite')
'cross by the sound of it' is the wordplay.
'cross' becomes 'rood' (term for a crucifix).
'by the sound of it' indicates a 'sounds like' (homophone) clue.
'rood' is a homophone of 'RUDE'.
'and' is the link.
(Other definitions for rude that I've seen before include "Impolite; basic" , "Ill-mannered; hearty" , "Offensive; unpolished" , "Impertinent" , "having no manners?" .)