A-axis

[ey-ak-sis]

noun, plural A-ax·es [ey-ak-seez] /ˈeɪˌæk siz/. Crystallography.

the horizontal crystallographic axis passing from front to back.

Compare B-axis, C-axis.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019