The Collaborative International Dictionary of English v.0.48:

Substile \Sub"stile`\, n. (Dialing)
   See Substyle.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]