In psychopharmacology, as opposed to military terminology, a psychotomimetic is a drug which causes symptoms analogous to those of a specific psychotic condition, normally schizophrenia. There's a great deal of overlap and blurred lines between propoer psychedelic/entheogenic drugs and psychotomimetics, but it's generally safe to say that there is a real difference. Everything pharmacologically considered a psychotomimetic would also be a psychotomimetic under the terminology outlined above by Tres Equis, but most would agree that the converse is not the case.
Probably the most famous psychotomimetic is the dissociative, phenycyclidine, or PCP, which is particularly well known in popular culture for the occasional bouts of violence, mixed with hysterical strength and lack of pain, that it produces in those who take it.
It's generally, though not universally, agreed now that the serontogenic psychedlics, (e.g. LSD, mescaline, psilocybin) are not psychotomimetic in their action as was originally presumed. LSD, in particular, was often described in early literature as producing effects nearly indistinguishable from those of schizophrenia, but the general consensus now is that while there are certain similarities, the symptoms and neurochemistry have fairly well-defined diferences.
One could make a case that the amphetamine family of drugs, and stimulants in general, can have a psychotomimetic effect, but this generally a result of people using them to avoid sleep for prolonged periods, and not a direct result of the drugs themselves. | 
