strict

(of rules) stringently enforced

• “hard-and-fast rules”

rigidly accurate; allowing no deviation from a standard

• “rigorous application of the law”
• “a strict vegetarian”

incapable of compromise or flexibility

not indulgent

• “strict parents”

unsparing and uncompromising in discipline or judgment

• “a parent severe to the pitch of hostility” H.G.Wells
• “a hefty six-footer with a rather severe mien”
• “a strict disciplinarian”
• “a Spartan upbringing”

severe and unremitting in making demands

• “an exacting instructor”
• “a stern disciplinarian”
• “strict standards”