"in a definite manner," 1580s, from definite + -ly (2). As a colloquial emphatic word, attested by 1931.
defile
defilement
definable
define
definite
definitely
definition
definitional
definitive
deflagration
deflate
)window.location='https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=byronic106@yahoo.com&lc=US&item_name=Donation+to +Help+Keep+Etymonline+Free+and+Open&no_note=0&cn=&curency_code=USD&bn=PP-DonationsBF:btn_donateCC_LG.gif:NonHosted'){kind=link}