Least a.  [Used as the superlative of little.] Smallest, either in size or degree; shortest; lowest; most unimportant; as, the least insect; the least mercy; the least space.
 Note: ☞ Least is often used with the, as if a noun.
    I am the least of the apostles.   --1 Cor. xv. 9.
 At least, or At the least, at the least estimate, consideration, chance, etc.; being no less than; hence, at any rate; at all events; even. See However.
 He who tempts, though in vain, at least asperses
 The tempted with dishonor.   --Milton.
    Upon the mast they saw a young man, at least if he were a man, who sat as on horseback.   --Sir P. Sidney.
 -- In least, or  In the least, in the least degree, manner, etc. “He that is unjust in the least is unjust also in much.” --Luke xvi. 10.
 Least squares Math., a method of deducing from a number of carefully made yet slightly discordant observations of a phenomenon the most probable values of the unknown quantities.
 Note: It takes as its fundamental principle that the most probable values are those which make the sum of the squares of the residual errors of the observation a minimum.