Green’s Dictionary of Slang

moo-moo n.1

[? Twi e-mumu, a person who is deaf and dumb]
(W.I.)

1. an extremely shy person, too nervous to speak out.

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[WI]Allsopp Dict. Carib. Eng. Usage.

2. a fool, a simpleton.

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[WI]cited in Allsopp Dict. Carib. Eng. Usage (1996).