Very forced smile concealing Charlie's gaffe (8)
I believe the answer is:
Here is my best explanation:
'gaffe' is the definition.
('solecism' can be a synonym of 'gaffe')
'very forced smile concealing charlie's' is the wordplay.
'very' becomes 'so' (I've seen this in other clues**).
'forced' indicates an anagram.
'concealing' means one lot of letters goes inside another.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'smile' anagrammed gives 'leism'.
'leism' placed around 'c' is 'lecism'.