Keywords: theory, theoretical, theorise
As a Noun
1. An idea or set of ideas that is intended to explain something. English = theory.
2. A set of ideas that relate to a particular subject. English = theory.
As a Verb or Adjective
1. To be based on or concerning the ideas and abstract principles of a subject, rather than the practical aspects of it. English = (be) theoretical.
2. To develop ideas about something in order to explain it. English = theorise.