Marginal  adj. 1 of or written in a margin. 2 a of or at the edge. B insignificant (of merely marginal interest). 3  (of a parliamentary seat etc.) Held by a small majority. 4 close to the limit, esp. Of profitability. 5 (of land) difficult to cultivate; unprofitable. 6 barely adequate.  marginally adv. [medieval latin: related to *margin]