be angry
嗔 centers on the expression of anger, specifically an angry outburst or glare. The single given meaning 'be angry' captures this focused emotional display.
嗔 combines 口 (mouth) with 真, which likely contributes the sound and may relate to the idea of fullness or intensity, suggesting an angry outburst from the mouth.
A mouth (口) that speaks truth (真) too bluntly can make people angry. Picture someone shouting harsh truths and causing anger.
For シン, imagine an angry person shin-ing a bright light into someone's eyes while shouting: shin -> シン, and the glare makes everyone angry.