probably    umēnga, umēngo, kūmbure
En-En dictionary 
umēnga     I think, it seems, one might say, probably
umēngo   I think, it seems, one might say, probably
kūmbure     perhaps, maybe, probably
 probably found in: Kirundi I (Study lessons)
lesson 91   Dependent Clauses
lesson 104   Uses of Nta
 probably found in: Kirundi II (Grammar)
chapter 3   Conditional Sentences – “if”