Well Chimera is a term for something that is made up of many things right? So really a Human and a horse (centaur) would count as a Chimera would it not? or must if have many heads as well?
Two different types of Chimera, one is the mythological beast. The other is a genetics term of a single organism having genetically distinct cells from two or more zygotes (fancy way of saying that it was made with two eggs or two sperm that fused together and so if you do a DNA test on different parts of the body you could find different DNA, although since in animal reproduction it all still occurs from the parents you aren't going to find dramitically different DNA sequences in one animal, can also apply to plants, viruses, and pretty much anything else that is made up of DNA)
And technically there is the third type, Mount Chimaera, which is believed to be the origin of the myth, although that is debated.
Edit: It's also worth noting that D&D Chimera's do have wings and they have hooves on the back legs (front body Lion, back body Goat) And in D&D it was the snake (which they depict as a dragon's head) that breathed the fire (or other breath attack depending on the type of dragon's head)