heat up

(verb) gain heat or get hot. Synonyms: heat, hot up, heat up. Example: "The room heated up quickly."

(verb) make hot or hotter. Synonyms: heat, heat up. Examples: "The sun heats the oceans." "Heat the water on the stove."

(verb) make more intense. Synonyms: heat up, hot up, screw up. Example: "Emotions were screwed up."