plane

English has five distinct planes, four of which are essentially the same word as plain. These come ultimately from Latin plānus, but preserve its ‘flat’ meanings rather than (like plain) its ‘clear’ meanings. Plane ‘flat surface’ [17] comes from Latin plānum, a noun use of the neuter form of the adjective; it is the plane from which aeroplane, and hence its abbreviation plane, were formed. Plane ‘carpenter’s smoothing tool’ [14] comes via Old French plane from late Latin plāna, a derivative of the verb plānāre ‘make level’, itself a derivative of plānus. Plane ‘flat’ [17] is an alteration of plain, on the model of French plan ‘flat’. And plane ‘glide, soar’ [17] comes from French planer, a derivative of plan ‘level surface’ (the underlying notion being of a bird soaring with level wings). The odd man out is plane the tree-name [14], which comes via Old French plane and Latin platanus from Greek plátanos, a derivative of platús ‘broad’ (source of English place, plaice, and platypus) – the reference being to its broad leaves. Platanus probably also underlies English plantain, as applied to the banana-like vegetable. => PIANO, PLAIN; PLACE, PLAICE, PLANTAIN, PLATE, PLATYPUS