I. ˈdau̇tlə̇s adverb
Etymology: Middle English doutelees, from doute doubt + -lees (adverb suffix), from -lees (adjective suffix) -less
1. : without doubt : unquestionably
was doubtless the smartest girl in her class
2. : in all probability : presumably
II. adjective
Etymology: Middle English doutelees, from doute doubt + -lees -less
1. : free from doubt : certain
one of the doubtless sources of many Shakespearean quotations — Notes & Queries
2. obsolete : free from fear or suspicion
pretty child, sleep doubtless and secure — Shakespeare
• doubt·less·ly adverb