There is no word which means the exact opposite of galaxy. A galaxy is a massive group of stars and other material, so you might be able to say that the opposite of a galaxy is a single star. However, this would be similar to saying that the opposite of a group of people is one person - which is not quite correct.
Single faith.
The opposite of a mass battle could be single combat : a duel or bout. There is no direct opposite meaning "not" a pitched battle.
Mispronunciation. In mathematical terms, the opposite would be a group of words, since expression can mean a group of mathematical symbols representing a number or quantity.
Regarding "single" to be unmarried, the opposite is a married person, or spouse.
An individual is a single organism belonging to a population, which is a group of individuals of the same species living in the same area and capable of interbreeding.
A group of organisms of the same species is called a population. A group of different species living together is called a community.
The opposite of a collective noun is a noun for a single person or thing. A collective noun is a word used to group a noun for two or more people or things; a singular noun does not form a group (or collection).
A group of individuals belonging to a single species that live together in a defined area is called a population. This population shares resources, interacts with one another, and contributes to the ecological dynamics of the area where they reside.
A population is a group of individual of a single species that simulataneously occupy the same general area. Population may increase or decrease.
A single individual is not used to describe a population. A population refers to a group of individuals of the same species living in a particular area.
A population refers to a group of individuals of the same species living in a specific area, while an individual is a single organism. Populations can exhibit collective characteristics, such as population growth or genetic diversity, whereas individuals are distinct entities that make up the population.
As a group, it is a population; a single person is a citizen. The people of a place are also called inhabitants; or a single person is an inhabitant.
The experimental group
a single person or group
The experimental group
taken