A horizontal component of a structure
Horizon
A Tasmanian shrub or small tree whose main trunk tends to lean over and grow horizontally, Anodopetalum biglandulosum
Perpendicular to the vertical; parallel to the plane of the horizon; level, flat
Relating to horizontal markets
Pertaining to the horizon
1667: As when the Sun new ris'n / Looks through the Horizontal misty Air — John Milton, Paradise Lost, Book 1, ll. 594-5
(wine tasting) involving wines of the same vintages but from different wineries
Of an interval: having the two notes sound successively.