To define is to place something in the class in which it belongs and then distinguish it from other members of the class. To describe is to name traits or qualities. Traits or qualities might (or might not) be part of a definition and might even be necessary, but they would not be sufficient.
I would add that a definition is in some sense substitutable for the thing defined. Even if in practice you would not say “I’d like to buy a piece of furniture used for sitting, often with four legs” or “Put that four-legged piece of furniture used for sitting over there,” you could, and it would be intelligible. You can’t do that with “black with a mesh back and rolly wheels.”
These principles apply mostly to nouns. You can’t really describe things other than nouns because only nouns have qualities. We typically define verbs by using synonyms and qualifiers (to walk is to move the body using the legs); adjectives by synonyms and nouns (funny is amusing or causing laughter), adverbs with a prepositional phrase such as “in a —- manner or way,” and prepositions, conjunctions, and other odd little bits with strangely convoluted explanations. I imagine there are few indeed who would seriously attempt to define a word such as “to” or “than.”