i-adjective
stiff; formal; ceremonious; strict
Describes a person, atmosphere, or manner that is overly formal, rigid, or lacking warmth and ease. Often used for social situations, rules, or writing style.
彼の挨拶はいつも堅苦しい。
His greetings are always stiff and formal.
このレストランは堅苦しくなくて、気楽に入れる。
This restaurant isn't stuffy, so you can go in casually.