• 苦くるしい — painful
• 苦にがい — bitter
• 苦労くろう — hardship, trouble
• 苦痛くつう — pain, suffering
• 苦手にがて — weak point, dislike
• 苦情くじょう — complaint
• 四苦八苦しくはっく — struggling desperately; in great distress

苦 combines 艹 (grass) with 古 (old). Originally referring to bitter-tasting herbs, it evolved to represent emotional pain or difficulty as well. It conveys bitterness both in taste and life experience.

苦くるしい時ときこそ、成長せいちょうの機会きかいです。
Times of hardship are opportunities for growth.

この薬くすりは少すこし苦にがいです。
This medicine is a little bitter.