Authorization or certification; a sanction, as given by a superior. / (countable) Something that provides assurance or confirmation; a guarantee or proof.

(organic chemistry) The phthalide (3Z,6S,7S)-3-butylidene-6,7-dihydroxy-4,5,6,7-tetrahydro-2-benzofuran-1-one or any of its derivatives that are used to counter migraine

(Canada, US, education) To study as or qualify in a subsidiary subject at college or university.

the quality or state of being irremovable