"Ardha" means "half" in Sanskrit. Since the full posture is difficult to be practiced, the half-posture, which is easier, is followed widely. This posture was first promoted by the great Yogi Matsyendranath, one of the founders of Hatha Yoga, and hence the name.
"Chakra" means "wheel" in Sanskrit. In the final position of this asana, the body is arched backward and resembles the rim of a wheel. Hence the name.
"Hala" means "Plough" in Sanskrit. This posture is called 'Halasana' because in the final position the body resembles the Indian plough.
"Paschima" means 'behind', 'back' or 'posterior' and 'Uttana' means to stretch out in Sanskrit. "Paschimotana" means stretching the posterior regions of the body.
"Shalabha" means "locust" in Sanskrit. The final position of this asana resembles a locust when it lowers its head to eat and raises its tail. Hence, the name.
"Sirsha" means "head" in Sanskrit. It is required to "stand on his head" in this asana and hence the name.
"Supta" means "asleep" in Sanskrit. "Supta Vajrasana" is lying down supine in Vajrasana.
"Tri" means "three", "Kona" means "angle", and "Trikona" means "triangle" in Sanskrit The straight legs with the floor between the feet resemble the three sides of a triangle in this asana. Hence the name.