Come in - it's an inflammation (9)
I believe the answer is:
enteritis
'inflammation' is the definition.
(I know that enteritis is a type of inflammation)
'come in it's an' is the wordplay.
I cannot quite understand how this works, but
'it's' could be 'tis' (I've seen this before) and 'tis' is found in the answer.
'an' could be 'i' (Roman numeral for one) and 'i' is present in the answer.
'come in' could be 'enter' (synonyms) and 'enter' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for enteritis that I've seen before include "illness" , "Inflammation of the intestine" , "gut problem" , "tummy upset" , "complaint" .)