ecto-

WordReference Random House Unabridged Dictionary of American English © 2026

ecto-, 

1. a combining form meaning "outer,'' "outside,'' "external,'' used in the formation of compound words:
   ectoderm.

Also,[esp. before a vowel,] ect-. 

• combining form of Greek ektós outside

Collins Concise English Dictionary © HarperCollins Publishers::

ecto- combining_form

1. indicating outer, outside, external

Etymology: from Greek ektos outside, from ek, ex out