The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
ner-1
DEFINITION:
Under, also on the left; hence, with an eastward orientation, north. Suffixed zero-grade form *n-t(r)o-.a.Nordic, north, from Old English north, north; b.northern, from Old English northerne, northern; c.Norse, from Middle Dutch nort, north; d.Norman1, Norwegian, from Old Norse nordhr, north. (Pokorny 2. ner- 765.) Compare deks-.
-t(r)o-. a. Nordic, north, from Old English north, north; b. northern, from Old English northerne, northern; c. Norse, from Middle Dutch nort, north; d. Norman1, Norwegian, from Old Norse nordhr, north. (Pokorny 2. ner- 765.) Compare deks-. 
