Synonyms for Additional:

adj.

accompanying (adjective)
affixed, in addition to, attached, supplemental, Adorning, adjoining, ornamental, companion, secondary, auxiliary, extra, besides, along with.
additional (adjective)
augmented, incremented, extended, larger, more, accrual, grown, expanded, increased, amalgamated, Annexed, enlarged, raised.
all (adjective)
extra.
attached (adjective)
Prefixed, merged, attached, accompanied, Spliced, bound, added, married, embellished, extra, Annexed, Suffixed, subscripted, augmented, related, extended, Hitched, connected, affixed, joined.
different (adjective)
else.
extra, supplementary (adjective)
other, supplementary, more, added, increased, affixed, further, new.
increased (adjective)
enlarged, elevated, extended, larger, augmented, multiplied, increased, inflated, swollen, expanded, magnified.

n.

too, together with something, in addition, also, as well. new, fresh, increase. additional (noun)
extra, further, another, else, supplemental, more, supplementary, added, other.
supplementary (noun)
new.

Other synonyms:

also. too. new. fresh. in addition
further.
Other relevant words:
new, another, fresh, in addition, as well, else, also, supplementary, other, increase, too, further.