*ser- 1

late 14c., conservacioun, "preservation of health and soundness, maintenance in good condition, act of guarding or keeping with care," from Latin conservationem (nominative conservatio) "a keeping, preserving, conserving," noun of action from past-participle stem of conservare "to keep, preserve, keep intact, guard," from assimilated form of com-, here perhaps an intensive prefix (see com-), + servare "keep watch, maintain" (from PIE root *ser- (1) "to protect").

Meaning "preservation of existing conditions" in any sense is from mid-15c. The word has been used since late 15c. in reference to English municipal authorities who had charge of rivers, sewers, forests, fisheries, etc. Specifically with reference to preservation of nature and wild places by 1909.

The phrase conservation of energy apparently was coined in French by Leibnitz in 1692; it is attested in English publications from early 18c. as conservatio virum vivarum or partially nativized versions of it. The exact phrase is attested from 1853. 

late 14c., conservatyf, "tending to preserve or protect, preservative, having the power to keep whole or safe," from Old French conservatif, from Medieval Latin conservativus, from Latin conservatus, past participle of conservare "to keep, preserve, keep intact, guard," from assimilated form of com-, here perhaps an intensive prefix (see com-), + servare "keep watch, maintain" (from PIE root *ser- (1) "to protect").

From 1840 in the general sense "disposed to retain and maintain what is established, opposed to innovation and change," or, in a negative sense "opposed to progress."

As a modern political tradition, "antagonistic to change in the institutions of a country," often especially "opposed to changes toward pure democracy," conservatism traces to Edmund Burke's opposition to the French Revolution (1790), but the word conservative is not found in his writing. It was coined by his French disciples (such as Chateaubriand, who titled his journal defending clerical and political restoration "Le Conservateur").

Conservative as the name of a British political faction first appeared in an 1830 issue of the "Quarterly Review," in an unsigned article sometimes attributed to John Wilson Croker. It replaced Tory (q.v.) by 1843, reflecting both a change from the pejorative name (in use for 150 years) and repudiation of some reactionary policies.

Strictly speaking, conservatism is not a political system, and certainly not an ideology. ... Instead, conservatism is a way of looking at the civil social order. ... Unlike socialism, anarchism, and even liberalism, then, conservatism offers no universal pattern of politics for adoption everywhere. On the contrary, conservatives reason that social institutions always must differ considerably from nation to nation, since any land's politics must be the product of that country's dominant religion, ancient customs, and historical experience. [Russell Kirk, "What is Conservatism," introduction to "The Portable Conservative Reader," 1982] 

Phrases such as conservative estimate (1874), in which it means "characterized by caution, deliberately low," make no sense etymologically. Related: Conservatively; conservativeness.