It seems that he is suffering from chuunibyou.

He often behaves strangely because of his 'chuunibyou' (middle-school 2nd year syndrome).

He is showing behavior characterized by 'chuunibyou'.

He was criticized for having a double standard.

These shoes have a double sole and are very durable.

His sword had a two-character inscription.

Binomial nomenclature plays an important role in biological taxonomy.

The iteration mark 〻 is frequently used in this ancient document.

We booked a double room.

Doublet is an important concept in linguistics.