Real Dictionary

sketch
countable noun: A sketch is a drawing that is done quickly without a lot of details. Artists often use sketches as a preparation for a more detailed painting or drawing.
countable noun: A sketch of a situation, person, or incident is a brief description of it without many details.
verb: If you sketch a situation or incident, you give a short description of it, including only the most important facts.
verb: If you sketch something, you make a quick, rough drawing of it.

sketch in American English
a simple, rough drawing or design, done rapidly and without much detail
to draw or describe quickly or in outline; make a sketch of
intransitive verb: to make a sketch or sketches
noun: a simply or hastily executed drawing or painting, esp. a preliminary one, giving the essential features without the details
transitive verb: to make a sketch of

sketch in British English
noun: a rapid drawing or painting, often a study for subsequent elaboration
verb: to make a rough drawing (of)