An Etymological Dictionary of Astronomy and Astrophysics

The chord through a focus and perpendicular to then major axis of a conic section.

Etymology (EN): L. latus “side;” rectum “straight,” → right.

Etymology (PE): Târ “thread, warp, string”
(related to tur “net, fishing net, snare,”
tâl “thread” (Borujerdi dialect), tân “thread, warp of a web,” from tanidan, tan-
“to spin, twist, weave;” Mid.Pers. tanitan; Av. tan- “to stretch, extend;” cf. Skt. tan- “to stretch, extend;” tanoti “stretches,” tántra- “warp; essence, main point;” Gk. teinein “to stretch, pull tight;” L. tendere “to stretch;”
Lith. tiñklas “net, fishing net, snare,” Latv. tikls “net;” PIE base *ten- “to stretch.”