gyron

from The Century Dictionary.

• noun In heraldry, a bearing consisting of two straight lines drawn from any given part of the field and meeting in an acute angle in the fesse-point.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Her.) A subordinary of triangular form having one of its angles at the fess point and the opposite side at the edge of the escutcheon. When there is only one gyron on the shield it is bounded by two lines drawn from the fess point, one horizontally to the dexter side, and one to the dexter chief corner.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun heraldry A triangular form having an angle at the fess point and the opposite side at the edge of the escutcheon.