Etymology
From Middle English burger, burgher, burghere, equivalent to burgh + -er (“inhabitant of”). Likely merged with and reinforced by Middle Dutch burgher (Modern Dutch: burger); from Middle High German burger (Modern German: Bürger); from Old High German burgāri (“inhabitant of a fortress”); derivative of burg (“fortress, citadel”), from Proto-West Germanic *burg, from Proto-Germanic *burgz, from Proto-Indo-European *bʰerǵʰ- (“fortified elevation”).
Compare also Old English burgwaras (“inhabitants of a burg, burghers, citizens”) and Serbo-Croatian purger. More at borough.