Obvious wart girl treated with a bit of Euthymol (4,5)
I believe the answer is:
writ large
'obvious' is the definition.
(similar in meaning)
'wart girl treated with a bit of euthymol' is the wordplay.
'treated with' indicates an anagram.
'a bit of' suggests taking the first letters.
The first letter of 'euthymol' is 'e'.
'wart'+'girl'='wartgirl'
'wartgirl' mixed up with 'e' makes 'WRIT LARGE'.
(Other definitions for writ large that I've seen before include "very obvious" , "exaggerated" , "on a mass scale" , "Emphasised" .)