This is the 3572nd most frequent Japanese word.
説
"説" (setsu) means "theory," "view," or "explanation."
In this sentence, the word '説' is used as a part of '説得力', which means 'persuasive power'. It refers to the ability to convince others about a particular topic or viewpoint.
その話には説得力があります。
That story has persuasive power.
Here, '説' is part of '学説', meaning 'academic theory'. It denotes reasoning or explanation within an academic or scientific context.
彼の学説は注目されています。
His academic theory is gaining attention.
Here, '説' is used as 'a theory or claim', indicating an opinion or viewpoint about the validity of the rumor in question.