horizontal

adj

1. Perpendicular to the vertical; parallel to the plane of the horizon; level, flat.

   “horizontal lines”

   “Power is derived from a British United Traction Limited "A"-type 150-h.p. six-cylinder horizontal diesel engine; this drives through a fluid flywheel, and thence through a free wheel unit to a four-speed epicyclic gearbox.”

   “[…] a pair of pauldrons with the light horizontal bar which in later years developed into the high neckguard of the sixteenth century; numbers of gauntlets, visors of helmets, and other pieces, the handling of which is a sheer joy […]”

2. Relating to horizontal markets
3. (archaic)Pertaining to the horizon.

   “As when the Sun new ris'n / Looks through the Horizontal misty Air”

4. Involving wines of the same vintages but from different wineries.
5. Having the two notes sound successively.
6. (euphemistic)Relating to sexual intercourse.

   “horizontal tango”

   “Comparing a man who inspires you intellectually and makes you laugh with a guy who fulfils all your horizontal desires means you’re not comparing like with like.”

7. Being or relating to the transmission of organisms between biotic and/or abiotic members of an ecosystem that are not in a parent-progeny relationship.

   “Infectious agents may spread by horizontal transmission.”

noun

1. A horizontal component of a structure.
2. Horizon.
3. A Tasmanian shrub or small tree whose main trunk tends to lean over and grow horizontally, Anodopetalum biglandulosum