mach / moc / mock [mɒk]
mach – n. – 1. the ratio of the speed of a body to the speed of sound in the surrounding medium; 2. Indicating the speed of sound, i.e., Mach 2 is twice the speed of sound
moc – n. – a soft-soled leather shoe used by North American Aboriginals, trappers and backwoodsmen
mock – n. & v. – n. – 1. a practise form or examination, procedure etc.; 2. a sham imitation without the intent to deceive; v. – 1. mimic; 2. ridicule or scorn