Managed to wet a line the last two hours of sun on Sunday, caught a 12" (what I believe to be) rainbow. However, I have been told that there are steelhead, could this have been a steelhead? This little guy went after a #6 General Practitioner!
The term "rainbow" usually refers to resident fish that don't migrate down to the salt water. Your fish sounds like a juvenile steelhead that has not yet migrated down to the salt water. It's the same species, but with a different life cycle. Steelhead typically spend a couple of years in fresh water before migrating downstream and spending several years in the ocean.
The vast majority of "rainbows" in rivers flowing into Puget Sound are in fact juvenile steelhead, except for those above impassable falls, such as Snoqualmie Falls.