marginal

adjective

• 1relating to or at the edge or margin:marginal notes
• relating to water adjacent to the land’s edge or coast:water lilies and marginal aquatics

• 2minor and not important; not central:it seems likely to make only a marginal difference the cost is negligible, less than marginal
• (of costs or benefits) relating to or resulting from small or unit changes: the issue is to estimate the marginal benefit from the increased frequency of screening examinations against the marginal increased cost
• (of taxation) relating to increases in income: the marginal tax rates on these incomes rise to as much as 80 per cent in some republics

• 3(of a decision or distinction) very narrow; borderline:a marginal offside decision
• British (of a parliamentary or council seat) held by a small majority and therefore at risk in an election.
• close to the limit of profitability, especially through difficulty of exploitation:marginal farmland

noun

• 1British a seat in a parliament or on a council that is held by a small majority and is at risk in an election: she is defending a key marginal for the Tories

• 2a plant that grows in water close to the edge of land: remove any dead foliage on water lilies and marginals