• 強烈きょうれつ — intense; powerful; striking
• 猛烈もうれつ — fierce; violent; extreme
• 烈火れっか — raging flames; blazing fire
• 烈士れっし — noble hero; “fierce spirit” person
• 壮烈そうれつ — heroic and intense; brave and tragic

The bottom part is the “fire” radical, れっか — flames burning down. The top part gives the sound レツ. Together, 烈 means heat so strong it rages or explodes — fierce, intense, violent.