The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
wr-o-
DEFINITION:
True, trustworthy. Oldest form *wr1-o-. Derivatives include warlock and verdict. 1.warlock, from Old English wr, faith, pledge, from Germanic *wra-.2.veracious, verism, verity, very; aver, verdict, veridical, verify, verisimilar, voir dire, from Latin vrus, true. 3. Normal grade *wero-, from *wer-o-, in Celtic compound *ro-wero- (see per1). (Pokorny 11. er- 1165.)
r
-o-
r, faith, pledge, from Germanic *w
er- 1165.) 
