コツコツ
kotsukotsu

To-Adverb

1. steadily; unflaggingly; untiringly; laboriously; diligently

Onomatopoeia
かれはこつこつ事実 じじつ調 しらべていた。
karewa kotsukotsu jijitsuo shirabete ita.
He was patiently digging for facts.
To-Adverb

2. knocking; tapping; clicking; drumming

Onomatopoeia
だれかがドアをこつこつとたたいている。
darekaga doao kotsukotsuto tataite iru.
Someone is tapping at the door.
Other forms: