To avoid confusing these words, remember this starting point: dialectic is a kind of rhetoric.
Rhetoric
Rhetoric, generally, means “ways of making an argument, presenting ideas, or persuading people”. The following sentences exemplify this meaning:
Your rhetoric does not make sense to me, so I do not agree.
The rhetoric of politicians often seems dishonest.
Attacking your opponent is bad rhetoric.
People seem to misunderstand the rhetoric of critical race theory.
Dialectic
Dialectic, on the other hand, is a very specific form of rhetoric, in which two opposing perspectives change each other, leading to a conclusion or new idea. One example of dialectic is the tradition of philosophical dialogues, such as those written by Plato, in which two philosophers argue in order to discover truth.
The philosopher Hegel is famous for his ideas about dialectic as a historical force, as well as a form of rhetoric; Hegel spoke of dialectic as a historical process in which opposing belief-systems transform each other; for example, one might talk about the dialectic of capitalism versus socialism in our world today, where capitalist countries are becoming more socialist, and socialist countries more capitalist. Karl Marx is also famous for his ideas about the Hegelian dialectic, which are central to Marxism.