MARGINAL adj. 1. Extremely small. "A marginal increase in core can decrease GC time drastically." See EPSILON. 2. Of extremely small merit. "This proposed new feature seems rather marginal to me." 3. Of extremely small probability of winning. "The power supply was rather marginal anyway; no wonder it crapped out." 4. MARGINALLY: adv. Slightly. "The ravs here are only marginally better than at Small Eating Place."