What is the difference between a Partner (silent or otherwise) and an investor?

Hmm, I'm not sure if this is quite what you were asking but hope it helps.

Taken from: The Law & Your Business: Legally, what's the difference between active investors and passive investors? (ABA Division for Public Education)

Active investors are your general partners or general members (along with you) of a limited liability company.

Passive investors who aren't involved in the day-to-day operations are your limited partners, or limited members of your limited liability company, or shareholders of your corporation.

So basically partners (which can be called investors but active investors according to what's above) are involved in the business and investors are just shareholders or just shares a part of the financing.

A silent partner would be about the same as an investor I think. Someone that has a part in the financing area but not with managing or so forth of the business.