Thumbnail

Origin

thumb + nail. The phrase thumbnail sketch was first attested 1852. Verb sense attested 1930s.

Full definition of thumbnail

Noun

1. The fingernail on the thumb.
2. A rough sketch (e.g., the size of one's thumbnail).
3. (chiefly computing) A small picture, used as a compact representation of a larger image.

Verb

1. (transitive) To describe concisely.