「一生懸命」(isshoukenmei) means doing something with one's utmost effort, wholeheartedly, or diligently. It describes a very serious and committed approach to a task. Example: 彼女は毎日一生懸命日本語を勉強しています。(She studies Japanese very hard every day.)

全ての力を尽くして、真剣に取り組む様子。