The Collaborative International Dictionary
substile
Substyle \Sub"style`\, n. (Dialing)
A right line on which the style, or gnomon, of a dial is
erected; being the common section of the face of the dial and
a plane perpendicular to it passing through the style.
[Written also substile.]
--Hutton.
Wiktionary
substile
n. (alternative form of substyle English)