Synonyms for Initially:

adv.

all (adverb)
Ab Initio.
at first (adverb)
originally, at the beginning.
firstly (adverb)
primarily.
initially (adverb)
maidenly, originally, formatively, firstly, preparatorily, Preliminarily, Aboriginally.

adv

firstly (adverb)
originally, firstly, primarily.
initially (adverb)
maidenly, originally, formatively, firstly, preparatorily, Preliminarily, Aboriginally.
in the beginning (adverb)
primarily.

n.

front end, new, early, from the get-go, all along, inaugural, opening, original, initial. at first (noun)
at first at first, at the beginning.
initially (noun)
at first, Ab Initio, at the start.

Other synonyms:

Other relevant words:
at first, early, at the start, Ab Initio, initial, at the beginning.