megaphone

Short definition from Wiktionary

Noun

1. 1
   A portable, usually hand-held, funnel-shaped device that is used to amplify a person’s natural voice toward a targeted direction.
2. 2
   Mouthpiece or promoter; one who speaks for or publicizes on behalf of another.
3. 3
   A cytotoxic neolignan obtained from the laurel Aniba megaphylla.

Verb

1. 1
   To use a megaphone; to speak through a megaphone.