not in the least Definition

least
adj

1. Smallest; slightest; denoting the smallest number or amount.

Thesaurus: fewest, smallest, lowest, last, merest, poorest, slightest.

adverb

1. In the smallest or lowest degree.

pronoun

1. The smallest amount.

Example: I think he has least to offer

Idiom: at least

If nothing else; at any rate.

Not less than.
Example: at least half an hour late

Idiom: not in the least (not in the least bit)

Not at all.

Idiom: the least

The minimum.
Example: The least you could do is visit from time to time

Etymology: Anglo-Saxon læst.