Waiter's struggling with English, so to speak (2,2,4)
I believe the answer is:
as it were
'so to speak' is the definition.
(synonyms)
'waiter's struggling with english' is the wordplay.
'struggling with' indicates anagramming the letters (the letters struggle or wriggle into a new form).
'english' becomes 'E' (abbreviation).
'waiters' mixed up with 'e' gives 'AS IT WERE'.
(Other definitions for as it were that I've seen before include "So to speak" , "you may say" , "Historically ungrammatical" , "Seemingly" , "As if it was actually so" .)