Only Charlie is beginning to make an embarrassing mistake (8)
I believe the answer is:
solecism
'an embarrassing mistake' is the definition.
'only charlie is beginning to make' is the wordplay.
'only' becomes 'sole' (synonyms).
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'beginning to' indicates taking the first letters.
The initial letter of 'make' is 'm'.
'sole'+'c'+'is'+'m'='SOLECISM'
(Other definitions for solecism that I've seen before include "Absurd or mistaken word or act" , "Error in grammar or manners" , "A mistake in the use of language" , "Social gaffe" , "Absurdity" .)