In heraldry, a bend is a band or strap running from the upper dexter (the bearer's right side and the viewer's left) corner of the shield to the lower sinister (the bearer's left side, and the viewer's right). Authorities differ as to how much of the field it should cover, ranging from one-fifth (if shown between other charges) up to one-third (if charged alone). The supposed rule that a bend should occupy a maximum of one-third of the field appears to exclude the possibility of three bends being shown together, but contrary examples exist. Outside heraldry, the term "bend (or bar) sinister" is sometimes used to imply illegitimacy, though it is almost never true that a bend sinister has this significance, and a "bar sinister" cannot, by its nature, exist.
Heraldic achievement of Hugh Fortescue, 1st Earl Fortescue, showing arms of Fortescue impaling Grenville. Baron: Azure, a bend engrailled argent plain cottised or; Femme: Vert, on a cross argent five torteaux.
Cotise: One-fourth the width of a bend; it appears only in pairs, one on either side (French: coté) of a bend, in which case the bend is said to be cotised as in the ancient arms of Fortescue and Bohun and in the more modern arms of Hyndburn Borough Council, England.
Riband or ribbon: Also one-fourth the width of a bend. It is also called a cost as in the arms of Abernethie of Auchincloch (Or, a lion rampant gules surmounted of a cost sable, all within a bordure engrailed azure — first and fourth quarters)
Scarp (or scarf): a bend sinister of one-half width.
The usual bend is occasionally called a bend dexter when it needs to contrast with the bend sinister, which runs in the other direction, like a sash worn diagonally from the left shoulder (Latin sinister means left). The bend sinister and its diminutives such as the baton sinister are rare as an independent motif; they occur more often as marks of distinction. The term "bar sinister" is an erroneous term when used in this context, since the "bar" in heraldry refers to a horizontal line.
The bend sinister, reduced in size to that of a bendlet (narrow) or baton (ending short of the edge of the shield), was one of the commonest brisures (differences) added to the arms of illegitimate offspring of European aristocratic lords. Such royal descent was considered a mark of honour, and in most of Europe, illegitimate children of nobles, despite having few legal rights, were customarily regarded as noble and married within the most aristocratic families.
This was the usual mark used to identify illegitimate descendants of the English royal family dating from fifteenth century, as in the arms of Arthur Plantagenet, 1st Viscount Lisle, illegitimate son of Edward IV of England. The full-sized bend sinister was seldom used in this way, and more recent examples also exist of bends sinister that have no connection with illegitimacy, such as in the arms of the Burne-Jones baronets. These markings were never subject to strict rules, and the customary English use of the bend, bendlet, and baton sinister to denote illegitimacy in this way eventually gave way to the use of different kinds of bordures.
Sir Walter Scott is credited with inventing the phrase bar sinister, which has become a metonymic term for bastardy. Heraldry scholar Arthur Charles Fox-Davies and others state that the phrase derives from a misspelling of barre, the French term for bend. Despite its not being a real heraldic symbol (a bar cannot actually be either dexter or sinister since it is horizontal), bar sinister has become a standard euphemism for illegitimate birth.
The phrase in bend refers to the appearance of several items on the shield being lined up in the direction of a bend, as in the arms of the ancient Northcote family of Devon: Argent, three crosses-crosslet in bend sable. It is also used when something is slanted in the direction of a bend, as in the coat of Surrey County Council in England.
Freeman, Jan (2009). Ambrose Bierce's Write It Right: The Celebrated Cynic's Language Peeves Deciphered, Appraised, and Annotated for 21st-Century Readers. Bloomsbury Publishing USA. ISBN978-0-8027-1970-6.