'Horizontally' definitions:

Definition of 'horizontally'

(from WordNet)
adverb
In a horizontal direction; "a gallery quite often is added to make use of space vertically as well as horizontally"

Definition of 'Horizontally'

From: GCIDE
  • Horizontally \Hor`i*zon"tal*ly\, adv. In a horizontal direction or position; on a level; as, moving horizontally. [1913 Webster]