'In least' definitions:

Definition of 'In least'

From: GCIDE

Least \Least\ (l[=e]st), a. [OE. last, lest, AS. l[=ae]sast, l[=ae]sest, superl. of l[=ae]ssa less. See Less, 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. [1913 Webster]
Note: Least is often used with the, as if a noun. [1913 Webster]
I am the least of the apostles. --1 Cor. xv. 9. [1913 Webster]
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. [1913 Webster]
He who tempts, though in vain, at least asperses The tempted with dishonor. --Milton. [1913 Webster]
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. [1913 Webster]