Synonyms for In essence:

adj.

practically (adjective)
basically.

adv.

all (adverb)
in principle, in theory.
basically (adverb)
essentially.
per se (adverb)
fundamentally.

n.

in essence (noun)
essentially, essential, substantial, basically, au fond, substantive, in theory, fundamentally, in principle.

Other synonyms:

in theory
in theory.