Lesser and Least

Lesser adjective - Having not so great importance or rank as another.

Least and lesser are semantically related. In some cases you can use "Least" instead an adjective "Lesser".

Least adjective - The superlative of `little' that can be used with mass nouns and is usually preceded by `the'; a quantifier meaning smallest in amount or extent or degree.

Lesser and least are semantically related. Sometimes you can use "Lesser" instead an adjective "Least".