Etimology
From Middle English probably, probabily, equivalent to probable + -ly.
adverb
probably (comparative more probably, superlative most probably)
In all likelihood.
Examples
“[…] the awfully hearty sort of Christmas cards that people do send to other people that they don't know at all well. You know. The kind that have mottoes […] . And then, when you see [the senders], you probably find that they are the most melancholy old folk with malignant diseases. […]”
Earless ghost swift moths become “invisible” to echolocating bats by forming mating clusters close […] above vegetation and effectively blending into the clutter of echoes that the bat receives from the leaves and stems around them. Many insects probably use this strategy, which is a close analogy to crypsis in the visible world—camouflage and other methods for blending into one’s visual background.
Related words
synonyms
as like as not
as likely as not
belike (archaic)
haply
in all likelihood
in all probability
likely
maybe
perchance
perhaps
possibly
presumably
coordinate terms
certainly
definitely
doubtlessly (sometimes synonymous)
doubtless (sometimes synonymous)
indisputably
indubitably
undoubtably
undoubtedly
unquestionably
without a doubt
without doubt