straight (adjective): free from curves, bends, angles, or irregularities
straight (adverb): in a straight manner  
strait (noun): 1) a comparatively narrow passageway connecting two large bodies of water; 2) a situation of perplexity or distress
—Merriam–Webster

When determining whether to use straight or strait, remember: strait is usually a noun, but straight can be an adjective or an adverb. This means straight works with nouns and verbs to describe them.

Examples of straight:
1. Morris has straight teeth.
2. Morris walks straight to the dentist.

In the first example, straight is an adjective that works with the noun teeth. In the second example, straight is an adverb that works with the verb walks.

Examples of strait:
1. The boat barely fit through the strait.
2. The crew was in dire straits when the boat started to sink.

In both examples, strait is a noun. The first example uses the first definition of the word. The second example uses the second definition of the word.

A note about jackets
The word for the white, strappy device used to restrain people is commonly misspelled. It is spelled: straitjacket. Also note that it is one word.

Quiz
Fill in the blank with either straight or strait. The answers are at the bottom.

1. The negative balance in Liz’s checking account showed she was in desperate financial _______s.
2. It took less time to run the _______ path than the curvy one.
3. Liz ran ______ to the candy shop.
4. The ship sailed _______ through the _______.
5. The men forced the patient into a _______jacket.

Answers:

1. strait (second definition) 2. straight (adjective) 3. straight (adverb) 4. straight (adverb), strait (first definition) 5. strait