early 15c., "a temporary halting or deprivation," from Latin suspensionem (nominative suspensio) "the act or state of hanging up, a vaulting," noun of action, from past participle stem of suspendere "to hang up, cause to hang, suspend," from assimilated form of sub "up from under" (see sub-) + pendere "to hang, cause to hang; weigh" (from PIE root *(s)pen- "to draw, stretch, spin"). Suspension of disbelief is from Coleridge:
A semblance of truth sufficient to procure for these shadows of imagination that willing suspension of disbelief for the moment, which constitutes poetic faith. ["Biographia Literaria," 1817]
Meaning "action of hanging by a support from above" is attested from 1540s. Meaning "particles suspended in liquid without dissolving" is from 1707. Suspension-bridge first recorded 1819 (earlier suspended bridge, 1796).