late 14c. as a classification in logic, from Latin species "a particular sort, kind, or type" (opposed to genus), originally "a sight, look, view, appearance," hence also "a spectacle; mental appearance, idea, notion; a look; a pretext; a resemblance; a show or display," typically in passive senses; in Late Latin, "a special case;" related to specere "to look at, to see, behold" (from PIE root *spek- "to observe"). From 1550s as "appearance, outward form;" 1560s as "distinct class (of something) based on common characteristics." Biological sense is from c. 1600. Endangered species is attested by 1964.