The Meia-Lua de Compasso (lit: half-moon compass) aka Rabo de Arria, is an attack that embodies the true element of Capoeira since it combines an evasive maneuver with a spinning kick. The transfer of power begins with the hand slamming into the ground and ending with the spin of the kicking heel. The power of the kick derives its energy from the similar centripetal force of a golf club swing. The transfer of power begins with the spin of the hand slamming into the ground and ending with the spin of the kicking heel. It has earned its place in capoeira as being called the "king of kicks". There is even a saying among capoeira mestres on how a capoeirista's general skill level can be determined on how well and fast they are able to execute a Meia lua de compasso. This video will show how effective this particular kick could be:
The name itself holds the main feature of the kick: the compass. When you're performing this kick, you point on the stationary leg, that acts as a pivot, and bending on it you kick with the other leg in a circle, turning on the stationary foot and helping your balance with hands. From the parallel stance in the ginga (cadera stance), bring one leg (usually not the last that has moved, but the other one) forward, always in a circling motion. You can start the Meia-Lua de Compasso from an orthogonal stance or from a back stance, turning 180° on the side of the stationary leg. Put your hands on the floor, in the middle of the legs (if doing two-handed, one hand would reach out to [and fingers pointed to] your opponent). Usually to have a better balance you point the fingers in the opposing directions, orthogonal to the line of the feet (i.e. if doing two-handed Meia-Lua de Compasso).
Shift your body weight on the leg you've just moved, bending the chest upon the thigh (keeping back relatively straight), and looking at the opponent from under the pelvis. Then raise the leg that has remained stationary until now, and kick in a circle line, turning on the foot on the floor. Make sure to lock your kicking leg to the base of your thigh, so your kicking leg is completely straight throughout the movement. You can exit the kick by putting the kicking foot in a parallel line or behind the front foot, in the ginga position, ready to restart the ginga.
In Capoeira - angola and regional - every movement has to be done the lowest possible; except in kicking and in esquivas, you never have to straighten the legs or stand up in the middle of a movement. Another important notion to keep in your head is that you always, no matter what position you may end up in, look at (and never lose sight of) the opponent and escape away from the kick (i.e. as opposed to escaping into the kick). The tutorial video below will show you how a good Meia-Lua de Compasso should be, courtesy of Contra-Mestre Barrãozinho of Axé Capoeira Vancouver and Professor Paraiba of Axé Capoeira Toronto: