A-axis

[ ey-ak-sis ]
/ ˈeɪˌæk sɪs /

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