from The American Heritage® Dictionary of the English Language, 4th Edition
- n. One that remains on the sidelines; a nonparticipant.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. One who stays on the sidelines; a spectator or nonparticipant.
- n. A beekeeper, neither a hobbyist nor a fully-fledged commercial operator, for whom beekeeping is a secondary source of income.
from The Century Dictionary and Cyclopedia
- n. A sidewinder, sidewiper, or massasauga.
sideline + -er (Wiktionary)