angulus

Ille terrarum mihi prter omnes / Angulus ridet—That nook of the world has charms for me before all else.

In the phrase angulus primi motus, angulus must be taken to mean angular motion.

Angulus isosceles, or Angulus quicrurus, is a triangle having equall shankes unto another.

Literally that; for the receding Porch is a deep 'angulus,' and its mid-pillar is the 'Head of the Corner.'