means A category of living things whose members can typically breed with one another, forming the basic unit biologists use to sort the diversity of life.

from From Latin 'species,' meaning 'a seeing, sight, appearance, kind,' built on 'specere,' to look — a cousin of 'spectacle,' 'inspect,' and 'spy.' The root idea is that a species is what something looks like, the visible 'kind' of a thing. It entered English by the 1300s as a logical term for a class within a wider 'genus,' and only later was drafted into biology to name nature's living types — ironic, since species turn out to be far harder to see clearly than the eye-rooted word suggests.