뜨겁다(tteu-geop-da, tteugeopda)
A state of very high temperature that is hard to touch or feels hot
When to use
hot coffee, hot water, fire heat, hot food
The nuance
Use 뜨겁다 when the temperature is high enough to strongly feel heat on the skin, typically for food, water, fire, etc.
미지근하다(mi-ji-geun-ha-da, mijigeunhada)
A temperature that is neither too hot nor cold, somewhat warm or lukewarm
When to use
lukewarm water, lukewarm drinks, lukewarm bathwater
The nuance
Use 미지근하다 to describe a temperature that is moderately warm or slightly cooled, not hot; often used for drinks, water, bathwater, etc.