(adjective): Referring to a door: barely open, cracked (entreaberta)

This adjective is used only in the predicate after connective verbs like "be," "seem," "become," and "remain". "Fritz left the door ajar," is acceptable but NOT "an ajar door."

It also does not compare and, though it may be used as an adverb, the suffix -ly is never attached. All English adjectives bearing the prefix a- exhibit the same behavior: "aglow," "afloat," "aboard," "adrift," etc.

"Ajar" also means "at odds" ("Sheila is ajar with her friends since piercing her eyelids") (this comes from the verb "jar" in the sense of "jarred loose."
Source: YourDictionary