YE OLDE CURIOSITY: ROOT OF PARTS OF SPEECH
Where do the names for the Parts of Speech come from?
You guessed it, from Latin; but where did Latin derive it from?
You may find the following reading interesting.
Article derives from the word articulus. Now, articulus is a diminutive of the 4a Decl. noun artus, -us, m., which means limb. Hence articulus, in the medical context, means a small limb attached to the body. But in the grammatical context of Latin, and all the other languages, article means something that is attached to the noun in the same way that limbs are attached to the body. Hence, an article never stands alone, it always needs a noun; grammarians say, "it accompanies" the noun. Hence: the apple, the rose, the man, etc.
Substantive derives from substantivus, -a, -um, which means "substance". The word is an adjective (of the first class), and adjectives cannot stand by themselves, they qualify a noun therefore they go next to the noun, either before or after the noun, but adjacent to it. There seems to be an apparent contradiction; I said "apparent", because the full definition ought to be substantivus verbum, now you have the adjective (substantivus) qualifying the noun (verbum) which means word, hence a word of substance, and if it is a word of substance it can stand on its own, hence it is a noun.
Adjective derives from adiectivus, -a, -um, which means "that which is added"; added to the noun to qualify it, or describe its characteristic more intensely, or describe possession, relativity, colour, size, quantity, specificity, etc. Adjectives are a bit like jokers in a game of cards. You can form adjectives almost at will, from nouns, verbs, pronouns, adverbs.