1.
unable to eat or drink hot things; sensitivity to hot food
Describes a person who cannot tolerate hot food or drinks. Literally 'cat tongue,' from the belief that cats dislike hot things.
Etymology
Literally "猫の舌" (cat's tongue). Based on the popular belief that cats cannot eat hot food.
Usage
Used as a self-description or to describe others. Most commonly appears with だ/です: 猫舌だ (I can't handle hot things). Can also be used as a modifier: 猫舌の人 (a person who can't handle hot food).
This is a widely understood and commonly used word in everyday Japanese. It is not considered childish or overly casual.