A specimen is a sample of something, like a specimen of blood or body tissue that is taken for medical testing. The noun specimen comes from the Latin word specere, meaning “to look.” Biologists collect specimens so they can get a better look at something to study it. The idea is that, with a good specimen, you can learn about an entire group: it's a good representation. That meaning is echoed in the slang use of specimen, a strong, healthy and attractive person.