bowstring, chord, hypotenuse
弦 centers on a taut line under tension: a bowstring, a musical chord, or the hypotenuse of a right triangle, all sharing the idea of a straight, stretched connection.
弦 combines 弓 (bow) with 玄, which likely contributes the sound and the idea of a dark, fine thread, together suggesting the taut string of a bow.
A bow 弓 with a dark, fine thread 玄 stretched across it: that's the bowstring. The same stretched line appears in a musical chord or the hypotenuse of a triangle.
For ゲン, imagine a genie stretching a bowstring: genie -> ゲン, and the genie's bowstring is pulled tight.
bowstring
orchestral music
music for strings; string music
string instrument; stringed instrument
reel for a spare bowstring
sine
first quarter moon; waxing half-moon
last quarter moon; third quarter moon; waning half-moon
bowstring
wind and string instruments; music
guitar string
single-stringed Japanese zither
qin (7-stringed Chinese zither); guqin; seven-stringed koto
shamisen; samisen
first quarter moon; waxing half-moon
last quarter moon; third quarter moon; waning half-moon
two-stringed koto
five strings; five-stringed instrument
cosine
three sides of right triangle (minor cathetus, major cathetus and hypotenuse)