con·serve 
(kən-sûrv)
(kən-sûrv)v. con·served, con·serv·ing, con·serves
v.tr.
1.
a. To protect from loss or harm; preserve: calls to conserve our national heritage in the face of bewildering change.
b. To use carefully or sparingly, avoiding waste: kept the thermostat lower to conserve energy.
2. To keep (a quantity) constant through physical or chemical reactions or evolutionary changes.
3. To preserve (fruits) with sugar.
v.intr.
To economize: tried to conserve on fuel during the long winter.
n. (kŏnsûrv′)
A jam made of fruits stewed in sugar.
[Middle English conserven, from Old French conserver, from Latin cōnservāre : com-, intensive pref.; see COM- + servāre, to preserve; see ser-1 in the Appendix of Indo-European roots.]
con·serva·ble adj.
con·server n.