Glossary Term Definition
A subhead set to one side of the text column, as opposed to a crosshead which is centered; commonly set flush left in the margin or indented.
Definition
A subhead set to one side of the text column, as opposed to a crosshead, which is centered. Sideheads are commonly set flush left in the margin or indented. They are a useful device for articulating the structure of a text while maintaining the flow of the main column.
Source
No access — Robert Bringhurst — p. 329:
A subhead set to one side of the text column.