Fr.: latus rectum
The chord through a focus and perpendicular to then major axis of a conic section.
L. latus "side;" rectum "straight," → right.
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."
Fr.: demi-latus rectum
Half the → latus rectum. For an ellipse, semilatus rectum has the expression l = b2/a, where a and b are semi-major and minor axes of the ellipse. It can also be expressed in terms of → eccentricity, e, as: l = a(1 - e2).