adverb, noun or participle which takes 'suru'
properly; in good shape; dignified
Describes a person's posture, appearance, or behavior as upright, neat, and dignified. Often used with する to mean 'pull oneself together' or 'straighten up'.
背筋を伸ばしてしゃんと座りなさい。
Sit up straight with good posture.
もう大人なんだから、しゃんとしなさい。
You're an adult now, so pull yourself together.