In a complete and detailed way, missing nothing.
“I would appreciate it if the matter could be thoroughly investigated.”
“Please review the attached documents thoroughly before our meeting.”
This adverb strengthens requests in CELPIP Writing Task 1, such as asking someone to 'thoroughly review' or 'thoroughly investigate' a problem. It shows you expect a careful, complete response rather than a quick, superficial one.
Synonyms: completely, carefully, fully