• 辛からい — spicy; hot (taste)
• 辛つらい — painful; tough; hard
• 辛口からくち — dry (taste); sharp-tongued
• 辛抱しんぼう — patience; endurance
• 辛苦しんく — hardships; toil
• 辛辣しんらつ — scathing; biting
• 香辛料こうしんりょう — spices

辛 is the radical itself. In ancient forms it resembled a marked needle, which led to senses like “to brand, to punish,” and by extension “bitter / harsh.” From taste (“spicy / bitter”) the meaning broadened to life situations (“hardship,” as in 辛つらい or 辛抱しんぼう).