From The Collaborative International Dictionary of English v.0.48 [gcide]:
Secondly \Sec"ond*ly\, adv.
In the second place.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
secondly
adv 1: in the second place; "second, we must consider the
economy" [syn: second, secondly]