[adv] without preparation or reflection; without a rational basis; "they bought the car blindly"; "he picked a wife blindly"
[adv] without seeing or looking; "he felt around his desk blindly"
BLINDLY is a 7 letter word that starts with B.
Webster's 1913 Dictionary
Definition:
\Blind"ly\, adv.
Without sight, discernment, or understanding; without
thought, investigation, knowledge, or purpose of one's own.
By his imperious mistress blindly led. --Dryden.
WordNet Dictionary