Wrap
The 'missing word' is wrap.
mass
soot
Duel and fuel are two rhyming words.
mass
kink
snap clap crap trap slap and more
Rock.
m
Ashy is a four-letter adjective that means covered in ash or ash-colored. Soot, dust, or slag are four-letter nouns meaning ash.
Shoe Shot Soot Coot Coat