A brother says that smoking is not haram but makruh. I believe that makruh and haram are synonyms, right? I would like to have the answer.

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
There is a difference between Makrooh and Haram in Islamic terminology. Haram (Unlawful) is what Allah has strictly forbidden. And the Makrooh (offensive) is what Allah has asked people to leave but has not strictly prohibited. What is described as Makrooh in Shari'a is lighter than what is described as Haram. You should know that smoking is not Makrooh, it is indeed Haram as it causes much harm and great damage to the human life, nobody can deny this. Please refer to fatwa: 81345 and 81589  for more details. Allah knows best.