blue
adjective
°Having a color shade close to blue.
noun
°The colour of the clear sky or the deep sea, between green and violet in the visible spectrum, and one of the primary additive colours for transmitted light; the colour obtained by subtracting red and green from white light using magenta and cyan filters.
°A blue dye or pigment.
verb
°To make or become blue.
°(metallurgy) To treat the surface of steel so that it is passivated chemically and becomes more resistant to rust.