Stupidly vain English easily tricked (5)
I believe the answer is:
naive
'easily tricked' is the definition.
The answer and definition are not the same part of speech. However, past participle verbs and adjectives occasionally define each other.
'stupidly vain english' is the wordplay.
'stupidly' indicates anagramming the letters.
'english' becomes 'e' (abbreviation).
'vain' with letters rearranged gives 'naiv'.
'naiv'+'e'='NAIVE'
Can you help me to learn more?
(Other definitions for naive that I've seen before include "Rather too simple and ingenuous" , "Foolish, inexperienced" , "Dewy-eyed" , "Simple in outlook" , "Rather too simple and gullible" .)