unthinkable, out of the question

Desolated is a door when no guests come knocking. Lit. To hang a net on the door and use it to catch sparrows (as no guests ever come).

practical question (problem)

a cheap seal

seldom lending or showing something precious because one values it

Montreal (the largest city in Quebec, Canada) / Montreal (an island in Quebec, Canada, the site of the city of Montreal) / Montreal (a river in Algoma district and Sudbury district, Ontario, Canada)

observatory (place where celestial bodies are observed)

Monrovia (the capital of Liberia)

hydrology

Kyūjitai form of 水文学: hydrology