How did certain words receive their name?

Wife and i were discussing how certain words came to be, like the word zipper. we all know what a zipper is, but how did it get its name? was the inventor name zip or zipper? how about the word “fly”? this word has several meanings, but only interested in the word fly as associated with a pair of pants. how did this word come to be? i have been told that the English language is the most difficult language to learn and understand. a single word can have several meanings and spelled differently. do you have a special word thats always puzzeled you?