しっかり (shikkari) means 'firmly,' 'steadily,' or 'properly.' This adverb describes doing something robustly, reliably, or thoroughly. It can refer to holding something tightly, thinking clearly, or carrying out a task correctly. For example, 「ドアをしっかり閉めてください。」(Please close the door firmly.)

しっかりは「きちんと」「確実に」「強く」という意味の副詞です。物事を確実に行う様子を表します。例：「ドアをしっかり閉める。」