Philosophy is part of unusual sitcom (8)
I believe the answer is:
stoicism
'philosophy' is the definition.
(Stoicism is an example)
'is part of unusual sitcom' is the wordplay.
'part of' indicates putting letters inside (part of the inside).
'unusual' indicates anagramming the letters.
'sitcom' is an anagram of 'stoicm'.
'is' inserted within 'stoicm' is 'STOICISM'.
(Other definitions for stoicism that I've seen before include "phlegm?" , "Resignation" , "Patient acceptance of suffering and misfortune" , "Endurance of hardship without complaint" , "Quality of bearing difficulties without complaint" .)