presumption

/pri-ˈzəm(p)-shən/

Middle English presumpcioun, from Anglo-French presumption, from Late Latin & Latin; Late Latin praesumption-, praesumptio presumptuous attitude, from Latin, assumption, from praesumere

noun

  1. presumptuous attitude or conduct : audacity

  2. an attitude or belief dictated by probability : assumption

  3. the ground, reason, or evidence lending probability to a belief

idiom

  1. believing that

Thousands of people used this drug on the presumption that it was safe.