Definify.com

Webster 1913 Edition

adv.

In the last place; in conclusion.

at last; finally.

adv.

In the last place.

In the conclusion; at last; finally.

lastly ‎(not comparable)

(sequence) Used to mark the beginning of the last in a list of items or propositions.
Firstly, that's illegal; secondly, it has serious disadvantages; thirdly, it's not necessary; and lastly, did I mention that it's illegal?
(discourse marker) Used to signal that the speaker is about to yield control of the conversation.

(last in order): finally, last, last of all
(discourse marker): finally, to conclude, to sum up, in conclusion; ultimately, in the end, all in all, at last

sequence

discourse marker