温
This Chinese character means warm.
You can watch how to write this. - (「温」の書き順（筆順）動画 - 漢字書き順辞典)
There are 2 main ways to read this, "あたたかい (温かい)" or "おん".
"温かい (あたたかい)" is a "い" adjective which means warm.
When this is combined with other Chinese characters, this is often read as "おん".
For example, "温度 (おんど)" means temperature.
"度 (ど)" means degree in this context.
Water boils at 100 degrees and freezes at 0 degrees, and that is how the Celsius temperature was determined.
By Higashi-Mikawa Kyōjindō Shujin (東三河狂人堂主人)