Outer; external; on the outside.
[Greek ektos, outside.]
Most terms are in scientific use: the ectoderm (Greek derma, dermat-, skin, hide) is the outermost layer of cells or tissue of an embryo in early development; an ectoparasite is a parasite, such as a flea, that lives on the outside of its host; ectoplasm (Greek plasma, formation) is the more viscous, clear outer layer of the cytoplasm in amoeboid cells (it can also be a substance that appears during a spiritualistic trance); an ectomorph (Greek morphē, form) is a person with a lean and delicate build of body. The adjective ectopic, used in medicine to denote something in an abnormal place or position (as in ectopic pregnancy) comes from Greek ektopos, out of place. The opposite of ecto- is endo-. See also exo-.