As adjectives the difference between unfilled and unbilled
is that unfilled is not filled while unbilled is (business) not yet having been billed.
As a verb unfilled
is (obsolete) (unfill).
unfilled
English
Verb
(head)
(obsolete) (unfill)
unbilled
English
Adjective
(
-)
(business) Not yet having been billed
- an unbilled invoice