Unmarried parent is not the same (5)
I believe the answer is:
other
'not the same' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for other that I've seen before include "One may be significant" , "Throe (anag)" , "Different; alternate" , "Different; additional" , "else!" .)