What defines a plant?

As a noun, a living thing belonging to the vegetable kingdom. ("Asparagus is a plant.") As a verb, derived from the noun, it means to place a seed or seedling in the ground to enable it to grow. ("I planted four rows of beans today.") Figuratively the verb can also mean to fix or introduce into anything. ("The idea was planted in his mind") An adjective can be made of the first sense. ("The compost contains plant matter.") By extension from the figurative verb use, it can mean a spy placed in an organization. ("Walter was a CIA plant.")