Posthumorous isn't a "proper" word; it's a combination of POSTHUMOUS (no R) which means "after death" and HUMOROUS which means "funny". Literally, posthumorous means "after funny", which doesn't have a clear meaning. Possible meanings for posthumorous or "post humorous" include:
- Something that was funny but isn't funny anymore (from answers.com)
- Something that is funny only because someone else finds it funny (from urbandictionary)
- Funny items from newspapers e.g. typos
- A musician/band (see Myspace and Facebook)
- There's a web site posthumorous.com that seems to be about computer forensics.