Synonyms for In addition:

adj.

additional (adjective)
further.
extra (adjective)
further.
more (adjective)
likewise, And.

adv

additionally (adverb)
moreover.
also (adverb)
along with, not to mention, as well as, too, furthermore, together with, And, moreover, likewise, further, also, Including, besides, additionally.

adv.

also (adverb)
along with, not to mention, as well as, too, furthermore, together with, And, moreover, likewise, further, also, Including, besides, additionally.
further (adverb)
to boot, besides, moreover, as well as, also.
likewise (adverb)
too, furthermore, additionally.
more (adverb)
along with.

n.

in addition (noun)
additionally, to boot.

Other synonyms:

Other relevant words:
additionally, to boot.