横

horizontal (Western) writing

gammaridean amphipod (any small, shrimp-like crustacean of suborder Gammaridea)

horizontal beam; stringpiece; trave

sidestroke (swimming)

round mallet

arguing persistently

cross member; crosspiece

traversing horizontally; passing through laterally; running east to west

short and fat; pudgy; stocky

tunnel tomb (Kofun period)

abscissa

horizontal structural members (beams, girders, etc.) of a building

either side of a rikishi's mawashi

horizontal friction; strike-slip

Internet slang

butting in (to a discussion on a message board, mailing list, etc.); reply from someone who has butted in

half-pass (horse gait)

leg-yield (horse gait)

Computing

double-width size (of text)

joining both chopsticks together and using them as a spoon (breach of chopstick etiquette)

Slang

side boob (side of a woman's breast exposed by clothing)

cross-cut; crossline; transversal; transverse line

crossing boundaries (structural, organizational, etc.)

Oft. adverbially as 〜に

(running) abreast; side-by-side; in a row

neck and neck; (almost) equal

line abreast; rank