noun
the sun; sunlight; heat of the sun
Often used in contexts of drying, evaporation, or natural processing by the sun, as in 天日干し (sun-drying) or 天日製塩 (solar salt production).
洗濯物を天日に干す。
I hang the laundry out in the sun.
この塩は天日で作られたものです。
This salt was made by solar evaporation.