Is the singular "endeleo" used, and if so, how would the meaning be different from "maendeleo", given that "maendeleo" is translated as "development", not "developments"?
From what I understand, the MA class is used for many abstract nouns, plural only. It's also used for uncountable things (and abstract things are uncountable) . I think it is the case here - but I may have misunderstood. So maendeleo means both development and developments, and is always plural.