Unusual, retiring in Tipperary (4)
I believe the answer is:
rare
'unusual' is the definition.
(thesaurus)
'retiring in tipperary' is the wordplay.
'retiring' says the letters should be written backwards.
'in' says the answer is hidden in the clue.
'erar' is hidden in the letters of 'tipperary'.
'erar' back-to-front is 'RARE'.
(Other definitions for rare that I've seen before include "Excellent; uncommon" , "not dense" , "Very infrequent or scarce" , "Very lightly cooked, meat say" , "may be bloody" .)