I'm no expert, but browsing through some online PIE databases, I would pick the following root: 

PIE  "au-" with a suffixed form "au-ge" in Germanic:

Greek "au", "auti", "aute" (again, also), Latin "aut" (or), "autem" (but), Umbrian "ute, ote" (also), Gothic "auk" (then, but), Old Norse "auk" (also, and), Old English "eac" (also), Old High German "ouh" (and, also, but), German "auch" (also), Tocharian A "ok" (still, yet), "oki" (and), Irish "agus" (and, but), Welsh "ac" (and, with), Middle Welsh "ac" (usually and, but occasionally conveys meanings such as but, yet, although)

The English word "eke" comes from the PIE root "aug-" and its derivatives all convey the sense of "to increase, augment":

Old English "ecan", Old Saxon "okian", Old High German "ouhhon", Old Norse "auka", Gothic "aukan", Latin "augere", etc.


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