The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
er-1
DEFINITION:
To move, set in motion. Oldest form *1er-. I. Basic form *er-.1. Probably Germanic *ar-,*or-,*art(a), to be, exist. are1, art2, from Old English eart and aron, second person singular and plural present of bon, to be. 2. Perhaps Germanic suffixed form *er-n-os-ti-.earnest1, from Old English eornoste, zealous, serious. 3. Uncertain o-grade suffixed form *ori-yo-.orient, origin, original; abort, from Latin orr, to arise, appear, be born. 4. Suffixed o-grade form *or-sm-.hormone, from Greek horm, impulse, onrush. II. Enlarged extended form *rei-s-.1.rise; arise, from Old English rsan, from Germanic *rsan;2. Suffixed o-grade (causative) form *rois-ye-.a.rear2, from Old English rran, to rear, raise, lift up; b.raise, from Old Norse reisa, to raise. Both a and b from Germanic *raizjan. (Pokorny 3. er- 326; ergh- 339.)
1er-. 
on, to be. 2. Perhaps Germanic suffixed form *er-n-os-ti-. earnest1, from Old English eornoste, zealous, serious. 3. Uncertain o-grade suffixed form *ori-yo-. orient, origin, original; abort, from Latin or
r
-. hormone, from Greek horm
ran, to rear, raise, lift up; b. raise, from Old Norse reisa, to raise. Both a and b from Germanic *raizjan. (Pokorny 3. er- 326; ergh- 339.) 
