rigorous

Concise Oxford English Dictionary © 2008 Oxford University Press:
rigorous/ˈrɪɡərəs/

▶adjective

• 1 extremely thorough, exhaustive, or accurate.

• 2 (of a rule, system, etc.) strictly applied or adhered to.

  ■ adhering strictly to a belief or system.

• 3 harsh and demanding.

– derivatives
rigorously adverb,
rigorousness noun.

– origin ME: from OFr. rigorous or late L. rigorosus, from rigor (see rigor1).