一生懸命 (is-shou-ken-mei) is usually translated as something like “with utmost effort”.
The kanji are:
一 = one
生 = life
懸 = depends (amongst other meanings…)
命 = fate
A more literal translation might be: “doing something as if your life depends on it”.
Fun fact, 一生懸命 is actually a 四字熟語 (yo-ji-juku-go), or 4-character idiom!
This is a special kind of idiomatic phrase, made of 4 kanji as the name suggests.
There are thousands of these in Japanese and they often contain a small life lesson or moral message, similar to English sayings such as “you reap what you sow” and “the early bird gets the worm”.
However 一生懸命 (is-shou-ken-mei) is so common in daily conversation that it’s presented in Japanese language textbooks as just a normal adjective. I’d been studying Japanese for ages by the time I realised that it was actually a 四字熟語 4-character idiom.