The Collaborative International Dictionary
Triquetrum \Tri*que"trum\, n.; pl. Triquetra. [NL.] (Anat.) One of the bones of the carpus; the cuneiform. See Cuneiform (b) .
Wiktionary
n. A shape formed of three ''vesica piscis'', sometimes with an additional circle, a symbol of things and persons that are threefold, and a symbol of protection in Wicca.
Wikipedia
Triquetra (; Latin tri- "three" and quetrus "cornered") originally meant " triangle" and was used to refer to various three-cornered shapes. It has come to refer exclusively to a particular more complicated shape formed of three vesicae piscis (the leaf-like shape in between two equal diameter circles when both centers are on the circumference of the other circle), sometimes with an added circle in or around the three lobes. Also known as a "trinity knot" when parallel doubled-lines are in the graph, the design is used as a religious symbol adapted from ancient Celtic images by Christianity. It is similar to Odin's symbol, the valknut.
Usage examples of "triquetra".
Book of Shadows and sees that the triquetra symbol on the cover starts to glow.
The triquetra symbol on the cover of the Book of Shadows starts to glow brighter and quivers.
The triquetra symbol continues to quiver on the cover of the Book of Shadows.
Piper tucks the baby in with a blanket embroidered with the triquetra symbol on it.
Grams is leaning over the empty bassinet, touching the triquetra symbol on the blanket.
The cocktail napkin Paige was doodling on had a drawing of a rough version of the triquetra, the Power of Three.