Some traditionalists object to the word “of” after “myriad” or an “a” before, though both are fairly common in formal writing. The word is originally Greek, meaning 10,000, but now usually means “a great many.” Its main function is as a noun, and the adjective derived from it shows its origins by being reluctant to behave like other nouns expressing amount, like “ton” as in “I’ve got a ton of work to do.” In contrast: “I have myriad tasks to complete at work.”