The word bug in reference to a computer glitch has actually been used by engineers to refer to mechanical defects as far back as the 1870s, on the notion of an actual insect getting into the machine. And it was still used in that half-serious, half-joking sense through the early computing age⁠—notably, it was popularized in 1946 after scientists at the Harvard Computation Laboratory identified an actual moth in the machine as a cause of a malfunction in the Mark II computer. Unsurprisingly, the verb to bug meaning "annoy" also came from the insect, through a connection of them being perceived as irritating; as did to bug meaning "secretly electronically monitor" because of the idea of hidden cameras and microphones being the size of actual bugs. Finally, the noun bug has an unknown origin, but was probably somehow connected to the Middle English word bugge, meaning "something frightening" (this is also the source of bugbear and bugaboo​).

The word swoon has been around as a word meaning "faint" at least since its earliest attestation in a 1290 hagiographic manuscript, but at that point it had the rather ugly spelling suoweningue. Other ways of writing it at the time included swoʒene, swowene, swoune, and swowne, but in the fifteenth century a new version started to emerge without that second approximant sound and in the nineteenth century the figurative, romantic definition came about. The word came about as the past participle of the Old English verb swogan, which could mean "to make a sound" or "suffocate", and that is from the Proto-Germanic root swogana, also "make a sound". Finally, that's of uncertain origin, but there are relatives in other Germanic languages meaning "sigh" and "choke", so they all have to do with noises.

The word opera first started showing up in English contexts as a borrowed Italian word in 1648, and the first use of the Italian word in reference to the musical genre was in 1639. This is pretty interesting because the first opera is generally acknowledged to be Jacopo Peri's Dafne, which came out in 1597—so people didn't have a term for the type of composition for over forty years. Originally, the word meant "work" or "labor" in Italian, which seems a little weird until you think about how we talk about musical works and composers' magnum opuses (magnum opera in Latin). As I may have just revealed, opera comes from the Latin noun opus, also meaning "work". Finally, that's from the Proto-Indo-European root op, which meant "to work" and also forms parts of words like oeuvre, office, optimism, opulent, and cooperate.

The word balayage can have two meanings: in cosmetics, it's a technique for highlighting hair that's supposed to lighten it in a natural way, and in mathematics it's a method for reconstructing a harmonic function. Both of these definitions comes from the French word bayalage, meaning "sweeping". The fashion thing is a reference to the way in which the color is applied with a sweeping motion, and the math thing is called that because a mass is "swept out" from a closed domain onto a boundary.  Balayage is from the verb balayer, meaning "to sweep", and that's from the noun balai, meaning "broom". That's thought to either trace to the Old Breton word balan or the Gaulish word balano, which also meant "broom". According to Google NGrams, usage of balayage peaked in 1974 and has been on the decline since.

I mentioned in a recent blog post how the circumflex in French is frequently used to indicate the historical presence of the letter s in a word where it was lost, and I just wanted to elaborate on that. Right around the time of the Norman Conquest, the s sound began to disappear before consonants in the middle of words, which caused the vowels before them to lengthen. People needed some way to notate this change, so the circumflex was introduced by the Académie Française in 1740. Here are some instances of this:

• Fête and festival are a great example because they're both English words, one borrowed from modern French and one from Old French
  
• Same with hotel (from French hôtel) and hostel (from Old French hostel)
• Pâté and paste
  
• Château and castle

You get the idea. I think comparing these is really cool!