Aisle. An extension northwards or southwards of the nave, usually designed to cater for the changing liturgical needs of the 14th and 15th centuries, often built as the result of a donation. It may have its own altar at the eastern end, often forming a side chapel, perhaps even a chantry chapel.

More colloquially, the word is used by many English people to mean the central gangway of the nave running from west to east.