The Collaborative International Dictionary of English v.0.48:

Nightly \Night"ly\, adv.
   At night; every night.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Nightly \Night"ly\, a.
   Of or pertaining to the night, or to every night; happening
   or done by night, or every night; as, nightly shades; he kept
   nightly vigils.
   [1913 Webster]

WordNet (r) 3.0 (2006):

nightly
    adv 1: at the end of each day; "she checks on her roses nightly"
           [syn: nightly, every night]
    adj 1: happening every night; "nightly television now goes on
           until 3:00 or 4:00 a.m."