IPA: /əˈtɔːrn/
KK: /əˈtərn/
The agreement of a tenant to recognize a new landlord after a transfer of property ownership.
The attornment was necessary for the new landlord to establish their rights over the property.
Attornment is formed from "ad-" (meaning to) and "tornare" (meaning to turn). The word originally referred to the act of turning or acknowledging a new lord or landlord, particularly in the context of feudal law.
Think of 'turning' ('tornare') to acknowledge someone new ('ad-') — that's why attornment means recognizing a new authority.