Rigorous or severe in approach or enforcement.
Rules, at times, can be very strict and harsh.
A parent
severe
Rigorous or stringent.
Another word for very strict or harsh is stern.
He was a very strict and harsh ruler
Harsh
Severe
The guide words for "harsh" could be "hard" and "strict."
Crossword puzzles may include a synonym of harsh, and it may be severe.
Lamented or sternly
Severe.