Definition of "horizontal"

horizontal

/ˌhɒɹɪˈzɒntəl/

adjective
comparative more horizontal, superlative most horizontal
1. Perpendicular to the vertical; parallel to the plane of the horizon; level, flat.
2. (marketing) Relating to horizontal markets
3. (archaic) Pertaining to the horizon.
  Quotations
  As when the Sun new ris'n / Looks through the Horizontal misty Air
  1667, John Milton, “Book I”, in Paradise Lost. […], London: […] [Samuel Simmons], […]; republished as Paradise Lost in Ten Books: […], London: Basil Montagu Pickering […], 1873, lines 594-595
4. (wine) Involving wines of the same vintages but from different wineries.
5. (music, of an interval) Having the two notes sound successively.
6. (sex, euphemistic) Relating to sexual intercourse.
  Quotations
  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.
  2020 February 2, Mariella Frostrup, “One is a great guy; the other is good in bed. So who do I choose?”, in The Guardian‎
7. (biology) 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.
noun
plural horizontals
1. A horizontal component of a structure.
2. (geology) Horizon.
3. A Tasmanian shrub or small tree whose main trunk tends to lean over and grow horizontally, Anodopetalum biglandulosum