- oak (n.)
- Old English ac "oak tree," from Proto-Germanic *aiks (cf. Old Norse eik, Old Saxon and Old Frisian ek, Middle Dutch eike, Dutch eik, Old High German eih, German Eiche), of uncertain origin with no certain cognates outside Germanic.
The usual Indo-European base for "oak" (*derwo-/*dreu-) has become Modern English tree. Used in Biblical translations to render Hebrew elah (probably usually "terebinth tree") and four other words. The Old Norse form was eik, but as there were no oaks in Iceland the word came to be used there for "tree" in general.