to cut, to cleave,

Sagitta
n 1: a small constellation in the northern hemisphere between
Cygnus and Aquila and crossed by the Milky Way [syn: Sagitta]
2: any arrowworm of the genus Sagitta

Source: Webster's Revised Unabridged Dictionary (1913)

Sagitta \Sa*git"ta\, n. [L., an arrow.]
1. (Astron.) A small constellation north of Aquila; the
Arrow.

2. (Arch.) The keystone of an arch. [R.] --Gwilt.

3. (Geom.) The distance from a point in a curve to the chord;
also, the versed sine of an arc; -- so called from its
resemblance to an arrow resting on the bow and string.
[Obs.]

4. (Anat.) The larger of the two otoliths, or ear bones,
found in most fishes.

5. (Zo["o]l.) A genus of transparent, free-swimming marine
worms having lateral and caudal fins, and capable of
swimming rapidly. It is the type of the class
Ch[ae]tognatha.


http://www.castlesontheweb.com/glossary.html

http://www.encyclo.co.uk/define/Keystone

Boss - Central stone of arch or vault; key stone.
Boss stone Cheops pyramid
the mark of a builder stone mason

http://dictionary.die.net/boss

Bread heiroglyph - Thoth ?