The word "so" is a conjunction and an adverb that indicates a degree or extent. As a conjunction, it is often used to connect clauses, suggesting a consequence or result. As an adverb, it emphasizes the extent of something, often modifying adjectives or adverbs to mean "to such a great extent" or "very."
The word "so" originates from Old English "swa," which meant "in this manner" or "to this extent." Over time, its usage evolved in Middle English, retaining a similar form and meaning, leading to its current use in Modern English.