Rude sentry's edging away from royal greeting (4)
I believe the answer is:
curt
'rude' is the definition.
(I've seen this before)
'sentry's edging away from royal greeting' is the wordplay.
I cannot quite understand how this works, but
'royal' could be 'r' (abbreviation) and 'r' is found within the answer.
The remaining letters 'cut' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
(Other definitions for curt that I've seen before include "Snappy" , "Concise" , "Brusque, short" , "Brief and to the point" , "Brusquely succinct" .)