Is the word Swell slang or a nonsense word?

"Swell" is not slang or a nonsense word. It's a real word with a few different meanings:

* Adjective: Meaning "excellent" or "very good" (often used in a playful or informal way). This meaning dates back to the 19th century. Example: "That party was swell!"

* Noun: A wave, especially a large one, in the ocean. This meaning is older and dates back to the 16th century. Example: "The surfers rode the swell."

* Verb: To become larger or increase in size, usually in a pleasing way. Example: "The bread dough is swelling nicely."

While "swell" is sometimes used in a slangy way, it's a legitimate word with a history and established meanings.