Source : Webster's Revised Unabridged Dictionary (1913)

Lengthily \Length"i*ly\ (-[i^]*l[y^]), adv.
   In a lengthy manner; at great length or extent.

Source : WordNet®

lengthily
     adv : in a lengthy or prolix manner; "the argument went on
           lengthily"; "she talked at length about the problem"
           [syn: {at length}]