"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.
"Ut" means 'raised' and "kata' means "hips" in Sanskrit. This posture is known as "Utkatasana" because while practicing it, the heels and hips are raised.
"Vriksha" means "tree" in Sanskrit. In the final position of this asana, you have to stand still like a tree.