What is the anatomical name for the ankle bone?

The astragalus - which also happens to be the name of an herb!

This article is about the plant genus. For bone in the ankle, see talus bone.
https://en.wikipedia.org/wiki/Astragalus

Unless my two semesters of anatomy and physiology were all in vain, I believe the ankle bone is called the talus, where the tibia and fibula meet.

The talus bone or astragalus of the ankle joint connects the leg to the foot.

https://en.wikipedia.org/wiki/Talus_bone

The tibia and fibia above the ankle joint connect to the talus which is below.

http://www.finedictionary.com/Astragalus.html defines the astragalus as 'the ankle or hock bone, the bone which articulates with the tibia at the ankle'.

http://www.thefreedictionary.com/astragalus defines it as 'the bone of the ankle; the astragalus'.

https://www.vocabulary.com/lists/153232 defines it as 'the bone in the ankle that articulates with the leg bones to form the ankle joint'.

Various other website dictionaries give similar definitions, so it seems 'you pays your money and takes your choice'!

The main bone that makes up the ankle is called the talus. Behind the talus is the os trigonum, which is another part of the ankle, sometimes called the posterior ankle. These bones are supported by the calcaneus.

Talus and astragalus are the same thing.

http://www.bartleby.com/107/pages/page266.html

Henry Gray (1825–1861). Anatomy of the Human Body. 1918.

The Talus (astragalus; ankle bone) (Figs. 270 to 273). The talus is the second largest of the tarsal bones. It occupies the middle and upper part of the tarsus, supporting the tibia above, resting upon the calcaneus below, articulating on either side with the malleoli, and in front with the navicular. It consists of a body, a neck, and a head.