sheet vs picture plane

sheet and picture plane both are nouns.

Word	Noun	Adjective	Verb	Adverb
sheet	Yes	No	Yes	No
picture plane	Yes	No	No	No

As nouns, picture plane is a hyponym of sheet; that is, picture plane is a word with a more specific, narrower meaning than sheet:

sheet: (mathematics) an unbounded two-dimensional shape
picture plane: the plane that is in the foreground of a drawing or painting; coextensive with but different from the objective surface of the work

Other hyponyms of sheet include Cartesian plane, facet plane, midline, midplane, orbital plane, tangent plane.

sheet (noun)	picture plane (noun)
bed linen consisting of a large rectangular piece of cotton or linen cloth; used in pairs	the plane that is in the foreground of a drawing or painting; coextensive with but different from the objective surface of the work
(nautical) a line (rope or chain) that regulates the angle at which a sail is set in relation to the wind
a flat artifact that is thin relative to its length and width
a large piece of fabric (usually canvas fabric) by means of which wind is used to propel a sailing vessel
paper used for writing or printing
newspaper with half-size pages
any broad thin expanse or surface
(mathematics) an unbounded two-dimensional shape

sheet (verb)	picture plane (verb)
cover with a sheet, as if by wrapping
come down as if in sheets