The rules that use the vocabulary item "cnn" are:

<rotary_aircraft_type>

cnn chopper

cnn choppers

cnn copter

cnn copters

cnn helicopter

cnn helicopters

cnn helo

cnn heloes

<rotary_aircraft_type-sing>

cnn chopper

cnn copter

cnn helicopter

cnn helo

<rotary_aircraft_type-pl>

cnn choppers

cnn copters

cnn helicopters

cnn heloes