geometric figure, "oblique-angled equilateral parallelogram," 1570s, from French rhombe, from Latin rhombus "a magician's circle," also a kind of fish, which in Late Latin took on also the geometric sense. This is from Greek rhombos "circular movement, spinning motion; spinning-top; magic wheel used by sorcerers; tambourine;" also "a geometrical rhomb," also the name of a flatfish.
Watkins has this from rhembesthai "to spin, whirl," from PIE *wrembh-, from *werbh- "to turn, twist, bend" (source also of Old English weorpan "to throw away"), from root *wer- (2) "to turn, bend" (see versus). But Beekes connects rhombos to rhembomai "to go about, wander, roam about, act random," despite this being attested "much later," a word of no clear etymology.
In general use in reference to any lozenge-shaped object. Related: Rhombic.