Irritate some? Small number inside (5)
I believe the answer is:
annoy
'irritate' is the definition.
(I know that irritate can be written as annoy)
'some? small number inside' is the wordplay.
'some?' becomes 'any' ('any' can be similar in meaning to 'some').
'small number' becomes 'no' (abbreviation; 'small' indicates a short form).
'inside' means one lot of letters goes inside another.
'any' going around 'no' is 'ANNOY'.
(Other definitions for annoy that I've seen before include "eat" , "get angry" , "Irritate, needle" , "Anger" , "Vex" .)