The Collaborative International Dictionary of English v.0.48:

Erd \Erd\ ([~e]rd), n. [OE. erd, eard, earth, land, country, AS.
   eard; akin to OS. ard dwelling place, OHG. art plowing,
   tillage, Icel. ["o]r[eth] crop, and to L. arare to plow, E.
   ear to plow.]
   The earth. [Prov. Eng.] --Wright.
   [1913 Webster]

   Erd shrew (Zo["o]l.), the common European shrew (Sorex
      vulgaris); the shrewmouse.
      [1913 Webster]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

ERD
       Entity-Relationship Diagram


The Free On-line Dictionary of Computing (30 December 2018):

entity-relationship model
entity-relationship diagram
ERD

    An approach to data modelling
   proposed by P. Chen in 1976.  The model says that you divide
   your database in two logical parts, entities (e.g. "customer",
   "product") and relations ("buys", "pays for").

   One of the first activities in specifying an application is
   defining the entities involved and their relationships,
   e.g. using an entity-relationship diagram to represent a
   model.

   ["The entity-relationship model: toward a unified view of
   data", P.P. Chen, ACM Transactions on Database Systems 1:1 pp
   9-36, 1976].

   (2009-11-21)