horizontal

adjective

hor·​i·​zon·​tal ˌhȯr-ə-ˈzän-tᵊl 

ˌhär-

1

a

: of or relating to the apparent junction of earth and sky : situated near the horizon

b

: parallel to, in the plane of, or operating in a plane parallel to the horizon or to a baseline : level

horizontal distance

a horizontal engine

2

: relating to, directed toward, or consisting of individuals or entities of similar status or on the same level

horizontal mergers

horizontal hostility

3

medical : relating to or being transmission (as of a disease) by physical contact or proximity in contrast with inheritance

horizontal transmission of the hepatitis B virus

Genes are normally inherited from parents, but they can also be inserted into a genome by viruses, plasmids, and other foreign agents—a phenomenon called horizontal transfer.

—Stephan Reebs

compare vertical sense 4

horizontal noun

horizontality

ˌhȯr-ə-ˌzän-ˈta-lə-tē 

ˌhär-

noun

horizontally

ˌhȯr-ə-ˈzän-tᵊl-ē 

ˌhär-

adverb

Examples of horizontal in a Sentence

Recent Examples on the Web

Looking ahead, Maier argued that vertical and horizontal storytelling are increasingly influencing each other rather than siloed. —Lise Pedersen, Variety, 21 Nov. 2025

The two-story main house, built in 1964, has been extensively updated since Russell owned it, both honoring its midcentury roots and bringing in more modern elements such as smooth concrete walls and horizontal wood cladding. —Mark David, Robb Report, 19 Nov. 2025

Stability is maintained not through horizontal checks but through vertical, one-way channels of power. —Deng Yuwen, Foreign Affairs, 14 Nov. 2025

Delong is seen first swinging the sledgehammer in a horizontal movement, which police say is consistent with the victim standing. —Alia Shoaib, MSNBC Newsweek, 14 Nov. 2025

Word History

Etymology

see horizon

First Known Use

1555, in the meaning defined at sense 1a

Phrases Containing horizontal

• horizontal bar

Rhymes for horizontal

• consonantal
• periodontal
• quantal

Kids Definition

horizontal

1 of 2 adjective

hor·​i·​zon·​tal

ˌhȯr-ə-ˈzänt-ᵊl, 

ˌhär-

1

: of or relating to the horizon

2

: parallel to the horizon : level

3

: being on the same level

horizontally

-ᵊl-ē

adverb

horizontal

2 of 2 noun

: a horizontal line or plane

Medical Definition

horizontal

adjective

hor·​i·​zon·​tal ˌhȯr-ə-ˈzänt-ᵊl, ˌhär- 

1

: relating to or being a transverse plane or section of the body

2

a

: relating to or being transmission (as of a disease) by physical contact or proximity in contrast with inheritance compare vertical

b

: of or relating to horizontal gene transfer

horizontally

-ᵊl-ē 

adverb

Legal Definition

horizontal

adjective

hor·​i·​zon·​tal ˌhȯr-ə-ˈzän-təl, ˌhär- 

: relating to, directed toward, or consisting of individuals or entities of similar status or on the same level

horizontally adverb