Architecture
Architecture is both the process and the product of planning, designing, and constructing buildings or any other structures. Architectural works, in the material form of buildings, are often perceived as cultural symbols and as works of art. Historical civilizations are often identified with their surviving architectural achievements.
Design
Design is the creation of a plan or convention for the construction of an object, system or measurable human interaction (as in architectural blueprints, engineering drawings, business processes, circuit diagrams, and sewing patterns). Design has different connotations in different fields (see design disciplines below). In some cases, the direct construction of an object (as in pottery, engineering, management, coding, and graphic design) is also considered to use design thinking.
Planning
Planning is the process of thinking about the activities required to achieve a desired goal. It involves the creation and maintenance of a plan, such as psychological aspects that require conceptual skills. There are even a couple of tests to measure someone’s capability of planning well. As such, planning is a fundamental property of intelligent behavior. An important further meaning, often just called "planning" is the legal context of permitted building developments.
Design
The urge for good design is the same as the urge to go on living. The assumption is that somewhere, hidden, is a better way of doing things.
Attributed to Harry Bertoia, Knoll Design, p. 66 in: Carlotte & Peter Fiell (2005) 1000 Chairs. Introduction
Design
If the chief rules of good design were understood by the masses as they might be, nothing would do more to promote beauty, improve workmanship, add to the value of manufactures, and in many other ways further the general welfare and prosperity of the country. They are simple, easy to acquire, and should be taught with the alphabet.
Ernest Flagg, Small Houses: Their Economic Design and Construction (1922)
Design
Design is redesign.
Jan Michl (2002), in "On seeing design as redesign" (Scandinavian Journal of Design History 12, 2002: 7-23.)