When two or more words sound exactly the same but have different meanings, they’re called homophones. A common example is there, their and they’re. They may be pronounced exactly the same way, but they have entirely different definitions. The same is true with cord and chord.
During my daily journeys through the Internet a while back, I came across someone who wrote that he couldn’t find the “USB chord” for his printer. While it is certainly possible that this was little more than a simple typo, I suspect that the person didn’t even realize that “chord” is the wrong term to use in this context.
A cord is a long flexible string, rope or cable that is usually made up of several twisted strands. A cord is typically used to connect things. You might talk about the power cord for your television, for example, which connects your TV to a wall outlet. You might have an extension cord for your lawnmower and a USB cord (though “USB cable” is more common usage) for your printer. You might also be familiar with corduroy, which is a fabric of woven, twisted fibers. That’s why corduroy pants look like several cords all woven together, side by side. The umbilical cord is the structure that connects a mother to a fetus in her womb.
A chord, on the other hand, is a musical term that refers to a sound when a group of notes are all played together at the same time. There are chords that you play on the piano. Even in the context of video games, when you have to press two or more buttons simultaneously in Guitar Hero or Rock Band, this is also referred to as a chord. If you are looking at sheet music, then a chord will usually appear as three notes stacked on top of one another.
There are also a handful of common English idioms that make use of the word chord. If something “strikes a chord” with you, it means that it evokes some sort of reaction from you, typically an emotional response of some sort. You might be in agreement with the statement that is said or you might simply “like” what was heard.
English can be very tricky, so whenever you’re not quite sure how to spell something, take the time to look it up. Yes, good grammar still matters, especially in this digital age where we’ve come to rely on computers to do the checking for us. Sometimes, you just have to pull the cord and do it yourself.
Are the two words etymologically linked? It seems like they would have to be, considering the overlaps in uses. For example chord is a musical term, and many musical instruments make their sound using cords: indeed, the technical classification of string instruments is “chordophones”, which, aside from meaning instruments made using strings, seems to have the same root as chord as in a group of musical notes.
Oh, and I happen to love striking cords, specifically with hammers.