horizontal
adjectiveOPAL W
  /ˌhɒrɪˈzɒntl/
  /ˌhɔːrɪˈzɑːntl/
 - flat and level; going across and parallel to the ground rather than going up and down
enlarge image- horizontal lines
 - (informal) I was so tired, I just wanted to be horizontal (= lying down).
 
Oxford Collocations DictionaryHorizontal is used with these nouns:- arrow
 - axis
 - beam
 - …
 
Word Originmid 16th cent. (originally meaning something of or at the horizon): from French, or from modern Latin horizontalis, from late Latin horizon, horizont-, from Greek horizōn (kuklos) ‘limiting (circle)’. 
