Definition of horizontal adjective from the Oxford Advanced Learner's Dictionary

horizontal

adjective

ˌhɒrɪˈzɒntl horizontal pronunciation American

ˌhɔːrəˈzɑːntl horizontal pronunciation American

ˌhɑːrəˈzɑːntl

flat and level; going across and parallel to the ground rather than going up and downhorizontal lines (informal) I was so tired, I just wanted to be horizontal (= lying down). compare verticalhorizontally

ˌhɒrɪˈzɒntəli horizontally pronunciation American

ˌhɔːrəˈzɑːntəli horizontally pronunciation American

ˌhɑːrəˈzɑːntəli

adverbCut the cake in half horizontally and spread jam on one half.