1) Critically 2) Essentially 3) Fundamentally 4) Importantly 5) Irreplaceably 6) Momentously 7) Necessarily 8) Remarkably 9) Significantly 10) To a crucial degree 11) Very usefully 12) Vitally 1) Essentially 2) Significantly 
[adv] - to a crucial degree
crucially Extremely important because many other things depend on it; as with, The orchestra wants to win over fans and, more crucially, radio producers.
adverb to a crucial degree; `crucially important`; `crucially, he must meet us at the airport`