Dictionary of Medieval Names
from European Sources

Gemma f. Latin gemma 'gem, precious stone' or a vernacular feminine form of James (in England).

England
Latin
1240 Gemma (nom) StPaulDom p. 120
Italy
Latin
954 Gemma (nom) skinner p. 113; 1089 Gemma (nom) ibid. p. 115; 1348 Giemme (dat) INP 23; 1387 Gemma (nom) Venditti II-2053, Gemme (gen) ibid. II-2066
Cite as: J. Uckelman, S.L. Uckelman. "Gemma". In S.L. Uckelman, ed. The Dictionary of Medieval Names from European Sources, Edition 2017, no. 1. http://dmnes.org/2017/1/name/Gemma.