False one, screen in plastic (9)
I believe the answer is:
insincere
'false' is the definition.
(similar in meaning)
'one screen in plastic' is the wordplay.
'one' becomes 'I' (Roman numeral).
'plastic' indicates an anagram (plastic can mean easily moulded).
'screen'+'in'='screenin'
'screenin' is an anagram of 'nsincere'.
'i'+'nsincere'='INSINCERE'
(Other definitions for insincere that I've seen before include "Hollow" , "Untruthful" , "Less than honest" , "Not expressing genuine feelings" , "may be laying it on" .)