Släkthistoria för Gem
Gem Vad efternamn betyder
from Middle English Gemme Gimme also spelled Jemme Jimme. The Wakefield examples show that it was certainly a pet form of the male personal name German (see Jarman). Though direct evidence is lacking they were probably also Middle English pet forms of James also found in Middle English as Jemes Jeme and Jame. See also Gimson. from a Middle English female personal name Gemme Jimme latinized as Gemma Jemma. It is possibly an Old French pet form of Continental Germanic names like Germenberga and Germentrada but more likely a female use of the male name Gemme Jimme in (1) above.
Källa: The Oxford Dictionary of Family Names in Britain and Ireland, 2016