What's the difference between catacaustic and catacoustic?

Catacaustic

Definition:

• (a.) Relating to, or having the properties of, a caustic curve formed by reflection. See Caustic, a.
• (n.) A caustic curve formed by reflection of light.

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Catacoustic

Definition:

• (n.) That part of acoustics which treats of reflected sounds or echoes See Acoustics.

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