One only is noteworthy (8)
I believe the answer is:
singular
I believe this is a triple definition!
'one' is the first definition.
(synonyms)
'only' is the second definition.
(synonyms)
'is' acts as a link.
'noteworthy' is the third definition.
(thesaurus)
(Other definitions for singular that I've seen before include "Individual; extraordinary" , "One of a kind" , "number" , "Exceptional, one-off" , "Extraordinary, with reference to one" .)