Flame __, Substance That Slows the Spread of Fire

This page is the CodyCross answer for the clue below from Water Park, Group 750, Puzzle 2 (Aquatic Playground).

Question is: Flame __, Substance That Slows the Spread of Fire

and the answer is: RETARDANT

Word Meaning:

RETARDANT — (often in combination) Serving to impede (slow down) the action of something

Definitions from Wiktionary.