Definitions taken directly from www.Dictionary.com
Development: the act or process of developing; growth; progress:
Developing: undergoing development; growing; evolving.
1. to prepare the preliminary sketch or the plans for (a work to be executed), especially to plan the form and structure of.
[...]Design is inarguably a part of Development within the gaming industry (as well as many other industries) and therefore IS a form of Development. Development however, is comprised of multiple aspects some of which (NOT all) comprise elements of Design.
Therefore, Design is ALWAYS Development while Development does NOT always entail Designing.Oh boy... this threads is drowning into words. Actually, it's all very simple.
Development is about having a game finished and completed. That's the goal and the whole purpose. To have a playable (and preferably fun) game in the end.
Design is not a form of development, its only a part of development. A tool you use to make development process faster/easier/better. But alone design without a game in the end is nothing.