- spiralA curve that is the locus of a point that rotates about a fixed point while continuously increasing its distance from that point.
- spiroA polycyclic compound or system that contains a single atom as the only common member of two rings.
- spiricleOne of certain minute coiled threads in the coating of some seeds.
- spiriferAny of numerous species of fossil brachiopods of the genera †Spirifer and †Delthyris and allied genera in order †Spiriferida, in which the long calcareous supports of the arms form a large spiral, or helix, on each side.
- spirillumAny of various aerobic bacteria of the genus Spirillum, having an elongated spiral form and bearing a tuft of flagella.
- spiritrompeSynonym of haustellum (“sucking organ”).
- spirulaAny mollusk of the cephalopod genus Spirula, of which Spirula spirula is the only extant species.