Sentence:  <WSD>nut</WSD> straight = the best possible straight available (it can't be beat by any other straight, though it can still be beat by a better non-straight hand) 
Meaning of the word marked with <WSD> tags:  The best possible hand of a certain type, for instance: "nut straight", "nut flush", and "nut full house". Compare (t=the best possible hand available).