What is the difference between 'Corporate' and 'Corporation'?

After editing in banking and academia for 25 years, I can attest to the fact that 'corporate' is sometimes used as a noun in business jargon, either meaning corporation, or often, as an abbreviation for 'corporate customer' in one large American bank. However, it always rubbed me (a linguistically conservative American) the wrong way.

Corporate is a form of business. Basically, a corporate is a big company owned by shareholders. Corporation is a legal term. A corporation is the legal entity (a non-human legal person) that directly "owns" the corresponding corporate. Semantically, when one talks about business planning, cost and profits, company management, and other things related with running a big company, he should generally prefer the word "corporate". While strictly speaking, one can only strike a deal with a corporation (not a corporate), be employed by a corporation( not a corporate), or sue a corporation (not a corporate). But in informal language, the two words are often used interchangeably.