I do not find “dragonslay”, “dragon-slay”, “dragonslayer”, “dragon-slayer”, “dragonslayings,” or “dragon-slayings” anywhere in the most common 100,000 words of the Project Gutenberg corpus!  I will double check, as this is a quite unexpected finding.  Neither is it as a single word (even a two-word single entry) in the OED.

• 12.090 and they all began discussing dragon-slayings historical,
• 15.056 as the dragon-slayer,