Something signifying a huge amount in colloquial little typo (7)
I believe the answer is:
literal
'typo' is the definition.
(I know that typo can be written as literal)
'something signifying a huge amount in colloquial little' is the wordplay.
'something signifying a huge amount' becomes 'tera' (as in a terabyte).
'in' is an insertion indicator.
'colloquial little' becomes 'lil' (informal shortening of 'little').
'tera' put within 'lil' is 'LITERAL'.
(Other definitions for literal that I've seen before include "Ill rate (anag.)" , "Textual error" , "Tell IRA (anag) - word for word" , "Word-for-word" , "character fault?" .)