straight, strait

Straight or straight means not crooked or bent--
It's hard to draw a straight line without a ruler.
The shortest distance between two points is a straight line.
Fix your tie--it isn't straight.

Strait or strait ( rhymes with straight ) means a narrow channel of water connecting two larger bodies of water--
They sailed through the Bering Strait into the Arctic Ocean.
The Strait of Gibraltar is well-known to sailors.
Strait or strait is an archaic ( old-fashioned ) word for  narrow--
"Strait is the way, and narrow the gate..."

Now that you know that, you can say--
"The navigator fixed a straight course through the troublesome strait."

Note--a "straitjacket" is used to confine someone, usually a mental patient who is trying to harm him or herself--
The patient kept scratching at himself, so the nurses put him in a straitjacket.
Straitjacket is sometimes spelled straightjacket--
They confined him to a straightjacket when he wouldn't calm down.
Note # 2--"straits" may mean more than one strait--
They turned the ship around when the came to the Straits of Magellan.
"Straits" is also an unusual term meaning a difficult predicament--
The characters in a horror movie always find themselves in dire straits after the weird organ music.
Note # 3--to "straighten" something is to arrange it properly--
Straighten up the house; company's coming.
She straightened up the room.
"Straiten" means to constrict or limit, as in the phrase "straitened circumstances"--
The new taxes were sure to straiten their circumstances.
The family had been in straitened circumstances since the father lost his job.
Note # 4--a "canal" is also a narrow channel of water that connects two other bodies of water, but a canal is man-made--
Unfortunately, they were still digging a canal when plans were made for the new railroad.