Insect seen round about, invading the whole room (7)
I believe the answer is:
sanctum
'room' is the definition.
(I've seen this before)
'insect seen round about invading the whole' is the wordplay.
I cannot really see how this works, but
'about' could be 'c' (abbreviation for 'circa') and 'c' is found within the answer.
'insect' could be 'ant' (ant is a kind of insect) and 'ant' is present in the remaining letters.
'whole' could be 'sum' (sum is a kind of whole) and 'sum' is found in the leftover letters.
No letters remain.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sanctum that I've seen before include "Sacred or safe place" , "Holy area" , "somewhere private" , "SECOND PART OF 3" , "Private study" .)