By containing irritation, could become spiteful (6)
I believe the answer is:
bitchy
'spiteful' is the definition.
(thesaurus)
'by containing irritation' is the wordplay.
'containing' indicates putting letters inside.
'irritation' becomes 'itch' (I've seen this before).
'by' enclosing 'itch' is 'BITCHY'.
'could become' acts as a link.
(Other definitions for bitchy that I've seen before include "Unpleasant and spiteful like female dog" , "malicious" , "Speaking spitefully in manner of female canine" , "Catty" .)