Conservative means preferring to keep things as they are. A conservative approach, conservative in his tastes, a conservative estimate.
A conservative estimate is a deliberately cautious one, likely to be too low rather than too high, which is a very common use in reports. With a capital letter, Conservative means the British political party and its supporters, and small-c conservative is the useful phrase for somebody cautious who may vote any way at all. Note conservatism; and that conservative and conservationist are different words with a shared root.
1adjectiveconservativePreferring to keep things as they are.
“My grandparents are conservative and don't like changes to their daily routine.”
2adjectivedeliberatelyDeliberately cautious, of an estimate.
“That is a conservative estimate and the real figure is worse.”
conservative is a quality of caution.
Latin conservare means to preserve — con- plus servare, to keep. Conserve, preserve, reserve and observe are all the same verb, so a conservative is somebody who keeps things.
Latin
cōnservō — to preserve
Middle French
conservatif
English, today
conservative
Middle French conservatif, from Latin cōnservō (“to preserve”). Equivalent to conserve + -ative.
Etymology from Wiktionary, CC BY-SA