"a support, a rigid thing used to sustain an incumbent weight" (usually applied to something not forming a part of the object supported), mid-15c., proppe, probably from Middle Dutch proppe "vine prop, support; stop for a bottle," a word of unknown origin. Probably related to Old High German pfropfo, German pfropfen "to prop," which are perhaps from Latin propago "a set, layer of a plant" (see propagation). Irish propa, Gaelic prop are said to be borrowed from English.
"object used in a play," 1898, from props (1841), shortened form of properties (which was in theatrical use from early 15c.); see property.
"to support or prevent from falling by placing something under or against," mid-15c., probably from prop (n.1) or a related verb in Dutch. Meaning "support or sustain" in a general sense (especially a cause, institution, etc. at risk of failing) is from 1540s. Related: Propped; propping.