Synaesthesia is describing one sense in terms of another.
As with Raymond Chandler’s “She smelled the way the Taj Mahal looks by moonlight.”
Sight and sound seem to be interchangeable: colours are discordant or harmonious, and sad music dark.
Touch can be applied to sound–a gravelly voice–but rarely the other way round.
Taste can be widely applied–a delicious or sweet sound or a tasty fight–but the other senses are rarely applied to taste.
Smell is on its own–odious person, a stinking sight–but the other senses are rarely applied to it–which is why the Raymond Chandler quote is so pungent.
Synaesthesia can be most effective when a sense is applied to something abstract:
From Apocalypse Now: “I love the smell of napalm in the morning. You know, one time we had a hill bombed, for twelve hours. […] The smell, you know that gasoline smell, the whole hill. Smelled like … victory. Someday this war’s gonna end …”
Victory has no smell.
That idea of something smelling is surely widely applied (indeed, become a cliché): “Things didn’t smell right…I could smell a rat…