Hi,
René!
This is what I found:
GUMA (Gothic) means "mankind" (related to Latin "homo")
SINTHA (Gothic: sinth) also Old High
German "sind" (way, direction, journey), related to modern
German "Gesinde" (originally "companion in warfare") and "senden" (to send).
This is taken from:
Ernst Förstemann: Altdeutsche Personennamen (1906)
Henning Kaufmann: Altdeutsche Personennamen, Ergänzungsband (1968)
dtv Etymologisches Wörterbuch des Deutschen, München 1993