Clue: Something signifying a huge amount in colloquial little typo (7)
Answer: LITERAL
Explanation: Definition: typo
*An envelope ('in') of TERA (prefix, 'Something signifying a huge amount') in LIL ('colloquial little typo').* *Thanks to A Different Geof @1, the first to supply the omitted parsing … and to SueB @56 for the better version.