Thomas - Catholic - getting infected outside (7)
I believe the answer is:
sceptic
'thomas' is the definition.
(I've seen this before)
'catholic getting infected outside' is the wordplay.
'catholic getting' becomes 'c' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'infected' becomes 'septic' (similar in meaning).
'outside' indicates putting letters inside.
'c' inserted into 'septic' is 'SCEPTIC'.
Can you help me to learn more?
(Other definitions for sceptic that I've seen before include "Person who tends to disbelieve" , "Doubter; atheist" , "One questioning accepted opinions" , "He's hard to convince" , "Disbeliever" .)