IPA: /ˈvɜːtɪkli/
KK: /ˈvɜrtɪkli/
In a direction that goes straight up and down, rather than side to side or at an angle.
The flag was hung vertically on the wall.
Vertically → It is formed from "vert" (from Latin "vertere", meaning to turn) and the suffix "-ically" (meaning in a manner relating to). The word "vertically" describes something that is oriented or positioned in a manner that turns or extends up and down, as opposed to side to side.
Think of something that 'turns' ('vertere') to stand 'up and down' — that's why vertically means in an upright position.