The opposite of "lesser" is "greater or equal" and vice versa. Does the English language have single word antonyms for "lesser" and "greater"?
There is no single word antonym for lesser' to capture 'greater than or equal' (likewise for 'greater')
However a common shorter way to say the opposite of 'lesser' is to say
For example 'There are no less people in my group than yours' means my group may have exactly the same number or maybe more.
It is exactly the meaning you're looking for, but is not a single word, and also puts a large 'negation' burden on the reader/listener.
I believe your initial premise - The opposite of "lesser" is "greater or equal"- is a little incorrect and is causing some confusion. Qualities can be dissimilar without necessarily being opposites (which implies a certain complementary antagonism).
For example, even though things that are red aren't green, red wouldn't be considered the opposite of green. Similarly, one thing can be equal to another (which means it's not greater than the other), but that doesn't necessarily mean it's the opposite of being greater than the other.
I believe the antonyms for "lesser" and "greater" would respectively be "greater" and "lesser."
"Opposite of" is a relation that is meaningful only in a one-dimensional semantic cline with a center point, like tepid in the following:
- freezing - cold - cool - tepid - warm - hot - boiling
In this cline, freezing is the opposite of boiling, cold of hot, and cool of warm; but there's no opposite for tepid because it's a zero point, distinguishing negative from positive values. Very neat.
However, almost all semantic frames require more than one dimension. Comparing quantities is a good example of a multi-dimensional frame -- lesser and greater both presuppose at least two separate quantitative measures, and a comparison operation ranking them. This is much too ambitious to support a simple concept like "opposite".
For another example, what's the "opposite of" He may do it?
- He may not do it.
- He won't do it.
- He can't do it.
- He must do it.
or maybe something else? There are a number of dimensions involved with modals.
And we're not even talking about metaphorical uses, like the lesser of two evils.