Gouache and gosh 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.
Gouache is an opaque, water-based paint used in pre-digital graphic design illustrations, mockups, and art.
Gosh is an interjection. Interjections don’t really have a meaning. They are used to express surprise or astonishment, when a person is at a loss for words and making a simple observation. Gosh, that test was hard. Gosh, this rainy weather sucks. Interjections are safer words to use than expletives (swear words) in mixed company or people of all ages.
The following story uses both words correctly:
Gawain was just about to finish his latest portrait when he realized he was out of certain colors. This wouldn’t be a problem, except he promised the painting would be ready in a half an hour from now. “Oh my gosh! I’m out of white gouache!” he cried.