Warm

This Kanji is usually pronounced as "atata-" or "nuku" or "on"
(*There are exceptions) By itself, it means "(to) warm".

Some common forms of the word when used:

-atata-
温かい （atatakai/attakai): warm; mild
温める (atatameru/ nukumeru): to warm; to heat

-nuku-
温もり (nukumori): warmth

-on-
温室(onshitsu): Greenhouse
温暖化現象 (ondanka genjou): Greenhouse effect
地球温暖化 (chikyuu ondanka): Global warming
体温 (taion): Body temperature
温水(onsui): Warm water