Welcome to the new version of the Patents Manual. Please note there are changes to the numbering and sequence of the chapters and pages in the manual. You are encouraged to take the time to explore and familiarise yourself with this new structure. Dictionary principle

Date Published

What is the Dictionary principle? 

The dictionary principle is where the specification clearly states that a special meaning is to apply to certain words and phrases. This is acceptable if:

  • the special meaning is clearly expressed; or
  • it is clear that the specification is defining terms in a special way.

A special meaning may prevail over the plain (ordinary) meaning if the special meaning has been clearly defined. This is an exception to the principle that words should be given their plain meaning.

The nature of the dictionary principle is that if the patentee has used expressions which they have already adequately interpreted in the body of the specification, they are entitled to refer to the specification as a dictionary in which the meaning of the words they use has been defined (British Thomson-Houston Company Ld v Corona Lamp Works Ld (1922) 39 RPC 49 at page 67).

It must be clear that the specification is ‘setting up a dictionary’, that is, defining certain terms in a way that gives them a special meaning.

The patentee must have made their intention plain to those who read the specification where a particular word is to be read with a meaning set out in the specification (Minerals Separation North America Corporation v Noranda Mines Ltd (1952) 69 RPC 81 at page 93).

Amended Reasons

Amended Reason Date Amended

Published for testing

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