The Collaborative International Dictionary of English v.0.48:
Palette \Pal"ette\, n. [See Pallet a thin board.]
1. (Paint.) A thin, oval or square board, or tablet, with a
thumb hole at one end for holding it, on which a painter
lays and mixes his pigments. Hence, any other object,
usually one with a flat surface, used for the same
purpose. [Written also pallet.]
2. Hence: The complete set of colors used by an artist or
other person in creating an image, in any medium. The
meaning of this term has been extended in modern times to
include the set of colors used in a particular computer
application, or the complete set of of colors available in
computer displays or printing techniques.
3. Hence: The complete range of resources and techniques used
in any art, such as music.
4. (Anc. Armor) One of the plates covering the points of
junction at the bend of the shoulders and elbows.
5. (Mech.) A breastplate for a breast drill.
Palette knife, a knife with a very flexible steel blade and
no cutting edge, rounded at the end, used by painters to
mix colors on the grinding slab or palette.
To set the palette (Paint.), to lay upon it the required
pigments in a certain order, according to the intended use
of them in a picture. --Fairholt.