Sign on University Avenue, Berkeley, 2014.

There seem to be more and more instances of the adjective “everyday” being used where the adjective+noun (acting together as an adverbial phrase) “every day” should be used.  Everyday means: “Daily, quotidian, commonplace: happening every day.” Every day also means “daily,” but modifies a verb, not a noun.

Every Day vs. Everyday
The bus driver frowns at me every day. (adj. every modifies n. day; “every day” modifies v. frowns.)
It is an everyday occurrence. (adj. everyday modifies n. occurrence.)
Trick: If you can replace it in a sentence with “every night,” it’s two words. (“Everynight” isn’t a word.)

Similarly (as seen in the badly proofed sign pictured), “everyone” and “every one” are used differently. Everyone is a pronoun, meaning “every person.” Every one is an noun phrase, meaning “each,” often followed followed by a prepositional phrase describing “one”:

Every One vs. Everyone
Every one of his passengers dislikes him. (Both every and the prepositional phrase of his passengers act as adjectives describing one.) NB: This sentence is tricky in regard to subject/verb agreement: the root subject is one [singular], so the root predicate, dislikes, is correspondingly singular. Cf. the sentence:
All of his passengers dislike him.  All is plural, and therefore we use the plural verb dislike. One dislikes; all dislike.
Everyone dislikes him. (Everyone is a pronoun and the subject of the sentence, yet as above, uses one (singular) to determine the verb case.)
He is disliked by everyone. (Everyone is still a pronoun, but the object of the preposition by. The prepositional phrase by everyone acts as an adverb describing v. disliked.)

“Prepositional” is really hard to type correctly.