Etymology
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vena cava (n.)
Medical Latin, from Latin vena "vein" (see vein) + cava, from cavus "hollow" (from PIE root *keue- "to swell," also "vault, hole").
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cavity (n.)

"a hollow place, empty space in the body," 1540s, from French cavité (13c.), from Late Latin cavitatem (nominative cavitas) "hollowness," from Latin cavus "hollow" (from PIE root *keue- "to swell," also "vault, hole").

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trivet (n.)
three-legged iron stand, 12c., trefet, probably from a noun use of Latin tripedem (nominative tripes) "three-footed," from tri- "three" (see three) + pes "foot" (from PIE root *ped- "foot").
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talipes (n.)
"club-foot, deformed foot," from Latin talus "ankle" (see talus (n.1)) + pes "foot" (from PIE root *ped- "foot"). The notion seems to be "walking on the ankles."
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concave (adj.)
Origin and meaning of concave

"incurved," early 15c., from Old French concave (14c.) or directly from Latin concavus "hollow, arched, vaulted, curved," from con-, here perhaps an intensive prefix (see con-), + cavus "hollow" (from PIE root *keue- "to swell," also "vault, hole").

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pedicel (n.)
"footstalk of a plant," 1670s, from Modern Latin pedicellus, diminutive of pediculus "footstalk, little foot," diminutive of pedem (nominative pes) "foot," from PIE root *ped- "foot."
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cavern (n.)

"large, natural cave under the earth," late 14c., from Old French caverne (12c.) "cave, vault, cellar," from Late Latin caverna "cave," from Latin cavus "hollow" (from PIE root *keue- "to swell," also "vault, hole"). In Old English such a land feature might be called an eorðscræf.

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coe (n.)

"hut built by miners over a mine shaft," to store their equipment, etc., 1650s, from some source akin to Dutch kouw, German kaue in the same sense, from West Germanic *kauja-, an early borrowing of Latin cavea "hollow," from cavus "a hollow" (from PIE root *keue- "to swell," also "vault, hole").

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biped (n.)
"animal with two feet," 1640s, from Latin bipedem (nominative bipes) "two-footed," as a plural noun, "men;" from bi- "two" (see bi-) + pedem (nominative pes) "foot" (from PIE root *ped- "foot"). As an adjective from 1781.
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concavity (n.)

c. 1400, "a concave surface," from Old French concavit "hollow, concavity" (14c.) or directly from Latin concavitatem (nominative concavitas), from Latin concavus "hollow, arched, vaulted, curved," from con-, here perhaps an intensive prefix (see con-), + cavus "hollow" (from PIE root *keue- "to swell," also "vault, hole"). From 1570s as "state of being concave."

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