shiver, severe cold
凓 centers on intense cold that makes one shiver: a severe, biting chill.
凓 combines the ice radical 冫 with 栗, which likely contributes the sound and may suggest the shivering sensation of cold. The exact historical development is uncertain.
Ice 冫 beside 栗 (chestnut) suggests a chestnut tree in freezing weather, its branches trembling in the severe cold—a vivid image of shivering.
For リツ, imagine the shivering chestnut tree dropping its nuts with a sharp 'rits' sound as they hit the frozen ground: rits -> リツ.