Strait and straight are homophones and easily confused words. Homophones means words that sound the same, but are spelled differently.
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. Similarly, autocorrect on mobile phones might suggest one word instead of the other, it would be easy to do since both words start with “s-t-r-a-i.”
Strait is a noun. As a geographical term, it’s a a naturally formed narrow waterway connecting larger bodies of water. Examples around the globe including Alaska’s Bering Strait, The Strait of Gibraltar off Spain, and the Bosporus Strait in Turkey. There are many more listed here. A strait can also be a situation that resembles that waterway—involving tight financial budgets, tight timelines or deadlines, and therefore, stressful and emotionally intense situations. You’re in a strait if you don’t know if you’re going to be a success or make it out alive. So you can probably imagine what the phrase “dire straits” means: being in a really, really bad situation from which there’s possibly no escape or reprieve. [TRIVIA: Yes, it’s Mark Knopfler’s band name, circa 1970s-1980s. Short, catchy, has drama or intrigue=good band name!]
Straight is an adjective. It means a path that doesn’t waver or shift from one point to another, or another object that stays similarly rigid in its position or trajectory.
In slang, straight is synonymous with heterosexual. Straight-edge has been used to describe people who have a drug-free lifestyle. A “straight jacket” is a piece of clothing put on psychiatric patients to prevent them from hurting themselves or others. The sleeves do not have openings at the ends and are bound across the chest with fastenings.
The following story uses both words correctly:
Struan thought he was on a straight, predictable trajectory of wealth when he joined a snow crab fishing enterprise, but falling overboard near the Bering Strait during a fierce winter storm changed all that.