From Latin 'dependere' (to hang down from) — reliance as the image of being suspended from something above.
To rely on someone or something for support or sustenance; to be contingent on or determined by a particular condition or factor.
From Old French 'dependre,' from Latin 'dependere' (to hang down, hang from), composed of 'de-' (down, from) and 'pendere' (to hang). The literal Latin sense was physical: a chandelier depends from a ceiling, fruit depends from a branch. The figurative sense 'to rely on' developed from the image of hanging from something — if you depend on someone, you are suspended from their support, and without it you fall. The PIE
The physical sense of 'depend' — to hang down from — survived in English far longer than most people realize. As late as the seventeenth century, poets described curtains depending from rods and stalactites depending from cave ceilings. Milton used it in Paradise Lost. The 'rely on' sense gradually crowded