A primitive root; properly, to triturate (in a mortar), i.e. (figuratively) to agitate (by concussion) -- tremble.
H7322. ruph
[רָפַף] verb Po`el shake, rock (Aramaic רְפַף, move Gently; Arabic quiver, flash, throb; also Late Hebrew רִפְרֵף flutter, Arabic flutter, flap wings); — Imperfect3masculine plural יְרוֺפָ֑פוּ שָׁמַיִם עַמּוּדֵי Job 26:11.