It forms all or part of: circumlocution; colloquium; colloquy; elocution; eloquence; grandiloquence; interlocution; interlocutor; locution; locutory; loquacious; loquacity; loquitur; magniloquence; magniloquent; obloquy; soliloquy; somniloquy; vaniloquence; ventriloquism; ventriloquy.
It is the hypothetical source of/evidence for its existence is provided by: Latin loqui "to speak;" Old Irish ad-tluch- "to thank," to-tluch- "to ask;" Old Church Slavonic tloko "interpretation, explanation."
"funnel-like instrument for assisting hearing or magnifying the voice," 1878, coined (perhaps by Thomas Edison, who invented it) from Greek megas "great" (see mega-) + phone "voice" (from PIE root *bha- (2) "to speak, tell, say"). Related: Megaphonic. In Greek, megalophonia meant "grandiloquence," megalophonos "loud-voiced."