I think it's short for Jeremy. From the book To Kill A Mockingbird. Only derivation I know.
"Jem" can be a word in some contexts, such as being a given name or a slang term. However, it is not a commonly recognized word in standard English.
Jeremy Atticus Finch
no
Jem learns that a white mans word will always be accepted over a black mans word. Jem learned this from Atticus in the book To Kill A Mockingbird.
Jem! It was about living in Maycomb.
Scout repeatedly asks her father, Atticus, about the meaning of the word "nigger" and why people use it, showing her confusion and curiosity about the racial issues in her community.
Jem gets back at Scout by pushing her into a tire.
because mrs. dubose said that atticus "lawed for n word"
yes jem is courageous
Jem could not escape because his pants were pulled taut in the wire fence.
he attacks Jem which breaks Jem's arm, then is stabbed, presumably by Jem or Boo Radley, who brings Jem back home
Dill and Jem see the shadow of Atticus Finch when Jem is on the porch of the house.
a camellia flower, like the ones of hers that Jem destroyed earlier. She did that to show Jem that she wasn't as awful of a person as Jem (and Scout) believed she was.
Jem from Jem and the Holograms is a fictional character. Her real name is Jerrica Benton, who leads a double life as a music superstar.
Jem Evans was born in 1867.