Cupola and coupler are easily confused words.
The spell-check application of most word processing software programs would not catch a slip-up of these two words. Spell-check is looking for words that aren’t in its dictionary, and words that resemble words in its dictionary but are possibly spelled wrong. Spell-check isn’t perfect. It doesn’t know and can’t guess what word you wanted or what word you meant, it can only judge the words on the page. If you used words that are all spelled correctly, it gives you a pass anyway.
Autocorrect suggests words that start with the same letters. It’s suggesting what word you may want to save time, but quite often, its suggestions are pretty off base. They don’t help you out, but they do make you laugh.
Cupola (pronounced “koo-puh-lah”) is a noun; it’s Italian in origin. It means small dome or square structure on a roof that’s designed as a lookout, or to allow air or light in, or for a combination of purposes. [Turrets were discussed in another post. While turrets are often located at the corners of castles or buildings, cupolas can appear anywhere on top of a building. A turret could be topped with a cupola.]
Coupler (pronounced “cup-plerr”) is a noun. It means a device that enables two components to come together or work in unison. It may be a rod that enables two components to move together. A PVC coupler allows two pipes to join into it. In electronics, a coupler can also be a transformer that connects circuits.
The following story uses both words correctly:
Cuyler was struggling to decorate the museum’s elaborate Christmas light show. He had roped lights around the building and the curves of the crowning cupola. Unfortunately, when he hit the switch to test his work, it failed. It turned out several couplers weren’t working right, so the lights weren’t performing as desired.