Severe is a synonym of Strict. 
Exhaust is a type of Gas. Exhaust is a synonym of Weaken. Weaken is a synonym of Relax. Sofa can be used for Relax. 
Severe <--Synonym--> Strict 
Gas <--IsA-- Exhaust <--Synonym--> Weaken <--Synonym--> Relax <--UsedFor-- Sofa 