Here's why:
* Homophone: Words that sound the same but have different meanings and spellings (e.g., "to" and "too"). "Straight" doesn't have any words that sound exactly the same but have different meanings.
* Homograph: Words that are spelled the same but have different meanings and may or may not be pronounced differently (e.g., "bow" as in a knot and "bow" as in a weapon). "Straight" doesn't have any words that are spelled the same but have different meanings.
"Straight" is simply a word with one distinct spelling and meaning.