leastEnglishOxford American Thesaurusleast determiner I have not the least idea what this phrase could mean: slightest, smallest, minimum, minimal, minutest, tiniest, littlest. ▷antonyms greatest, most.□ at leastcheck in at least one hour before takeoff: at the minimum, no less than, not less than; as a conservative estimate, at rock-bottom; more than.