Incandescence (4)
(Other definitions for heat that I've seen before include "Toast" , "Energy that caues a rise in temperature" , "Preliminary race to qualify finalists" , "Hotness" , "eliminating round" .)
(Other definitions for fire that I've seen before include "Ready, aim . . . ." , "Sack; conflagration" , "There's no smoke without it" , "Flames; passion" , "... or combustion" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">incandescence</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for glow that I've seen before include "Emanate light" , "rosy colour" , "Gleam" , "Radiate or redden" , "Shine with warmth, emotion" .)