Related Clues:

• Sonic bounce
• Bounce off
• Cave comeback
• Off-the-wall product
• Cavern feature
• Sound in a long hallway
• It's said once but heard twice
• Mythical nymph
• Be a verbal rubber stamp
• Bounce off the wall, in a way
• She adored Narcissus
• Dolphin's navigation aide
• Do likewise
• Repeat verbatim
• Returning waves, of sorts