As adverbs the difference between lengthily and longly
is that lengthily is in a lengthy way, in a manner that is long and drawn out, especially in time while longly is (obsolete) with longing desire.
lengthily
English
Adverb
(
en adverb)
In a lengthy way, in a manner that is long and drawn out, especially in time.
longly
English
Adverb
(
en adverb)
(obsolete) With longing desire.
For a long time; wearisomely.
Usage notes
* The usual adverb corresponding to several adjective senses of (long) is itself also (long), not (term).