decline (v.) Look up decline at Dictionary.com
late 14c., "to turn aside, deviate," from Old French decliner "to sink, decline, degenerate, turn aside," from Latin declinare "to lower, avoid, deviate, to bend from, inflect," from de- "from" (see de-) + clinare "to bend," from PIE *klei-n-, suffixed form of *klei- "to lean" (see lean (v.)). Sense has been altered since c.1400 by interpretation of de- as "downward." Meaning "not to consent, politely refuse," is from 1630s. Related: Declined; declining.
decline (n.) Look up decline at Dictionary.com
early 14c., "deterioration, degeneration," from Old French declin (see decline (v.)).