dhreu- / Indo-European roots
To fall, flow, drip, droop.
▲ Derivatives include dreary, drowse.
1. Extended form *dhreus-. drizzle from Old English -drysnian (in gedrysnian, to pass away, vanish), from zero-grade Germanic derived verb *drus-inōn.
2. Extended o-grade form *dhrous-.
a. dreary from Old English drēor, flowing blood, from Germanic *drauzaz;
b. drowse from Old English drūsian, to be sluggish, from Germanic *drūsjan.
3. Extended zero-grade form *dhrub-.
a. drop from Old English dropa, drop, from Germanic *drupan;
b. droop from Old Norse drūpa, to hang down, from Germanic *drūpōn, to let fall;
c. drip from Middle English drippen, to drip, drop, from an unattested Old English *dryppan or another source akin to Old English droppa, drop, from Germanic geminated *drupp-;
d. Germanic *drup-, to drip, in compound *obisdrup- (see upo-).
4. Suffixed zero-grade form *dhrubh-yo-. lithotripter, lithotrity from Greek thruptein, to crumble.
[Pokorny dhreu- 274.]