Malicious, up itself play (8)
I believe the answer is:
spiteful
'malicious' is the definition.
(similar in meaning)
'up itself play' is the wordplay.
'play' indicates anagramming the letters.
'up'+'itself'='upitself'
'upitself' is an anagram of 'SPITEFUL'.
(Other definitions for spiteful that I've seen before include "Malevolent, wanting to hurt" , "Catty" , "Vindictive - malicious" , "Showing malice" , "With desire to hurt" .)