Koi and Coy are easily confused words. They are pronounced identically, “koy,” yet they mean very different things. One is a fish. One describes human behavior.
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.
Koi is a noun. It means large, colorful carp (often orange, red, white, and black) put in ponds in people’s yards. Koi fish are originally from Japan and similar climates in Asia.
Coy is an adjective. It means to behave in a shy, elusive, or secretive way. In the phrase “playing coy,” it can also mean a person who claims or pretends to not know more information about a particular subject than they actually do.
The following story uses both words correctly:
Kokone didn’t enjoy all the social occasions and parties that were a big part of her parents’ jobs. When strangers came to the house, she did the obligatory welcoming greetings, but then she disappeared to the koi pond in her parents’ garden. No one found her there, so she wasn’t stuck playing the antisocial or coy kid, which embarrassed her parents in front of their important associates.