Lesser means smaller or less important of two. The lesser evil, a lesser charge, to a lesser extent.
It goes only before a noun, never after a verb, so a thing cannot be lesser than something else. The lesser of two evils is the fixed phrase. In species names it means the smaller of a pair, as in the lesser spotted woodpecker.
1adjectivelesserSmaller or less important of two.
“He pleaded guilty to a lesser charge and avoided prison.”
lesser is a comparison.
From less + -er.
Etymology from Wiktionary, CC BY-SA