A Difficult Challenge (maybe Vertically So)

This page is the CodyCross answer for the clue below from Popcorn Time, Group 400, Puzzle 4 (Green Screen).

Question is: A Difficult Challenge (maybe Vertically So)

and the answer is: TALLORDER

Word Meaning:

TALL ORDER — (originally US, idiomatic) A big job; a difficult challenge.

Definitions from Wiktionary.