"one who participates, a partaker," 1560s, from French participant, from Latin participantem (nominative participans), present participle of participare "to share in, partake of" from particeps "sharing, partaking" (see participation).

late 14c., observacioun, "the performance of a religious rite," from Old French observation (c. 1200) and directly from Latin observationem (nominative observatio) "a watching over, observance, investigation," noun of action from past-participle stem of observare "watch over, note, heed, look to, attend to, guard, regard, comply with," from ob "in front of, before" (see ob-) + servare "to watch, keep safe," from PIE root *ser- (1) "to protect." Sense of "act or fact of paying attention" is from 1550s. Meaning "a remark in reference to something observed" is recorded from 1590s.

"sharing, having a share or part," late 15c., from Old French participant and directly from Latin participantem (nominative participans), present participle of participare "to share in, partake of," from particeps "sharing, partaking" (see participation).

1834, "of or pertaining to (scientific) observation," from observation + -al (1).

"participant in the movement for communal nudity," 1929, from nature + -ist. Earlier in other senses, including "naturalist" and "a physician who trusts entirely to nature for a cure" (1851). Related: Naturistic; naturism.

1650s, "fact of being worthy of comment," also "an act of observation" (a sense now obsolete), from remark (v.). The meaning "a verbal or written notice or comment" is from 1670s; the sense of "observation, notice" also is from 1670s.

"an advocate of or participant in revolution," 1710; see revolution + -ist. A supporter of the English Revolution of 1688 might be a revolutioner (1690s).

"capable of participating; having the quality of participating," 1650s, from participate + -ive. Earlier adjectives were participate (from Latin participatus), participant, both late 15c.