It means ‘staking all on something’. When was the last time you bet your sweet life or future on someone or something? This can be a very dicey proposition.
It is a combination of two words ‘乾坤’+’一擲’.
乾坤(ken-kon)=It implies heaven and earth. It is a very rare expression that even Japanese seldom use it. It’s because there is an easier word for this with the same meaning, it is 天地 (ten-chi).
一擲(it-teki)
‘一’ means one or single.
‘擲’ has various definitions but in this phrase, it means shot (other options: to strike or to hit)
Overall,
乾坤一擲 = Staking everything or playing an all or nothing game.
Therefore, it can give us an image of a very determined person pursuing a very risky or challenging task.
If you are interested in these Kanji, you may simply copy them from this website and use them as you please. Make them yours!