אֵין 'ayin "no one, nothing"
In Amos 2:11 in combination with זֹאת "this/thus" as a question = "isn't it so";
in 3:4 & 5, as one of a series of ways to ask rhetorical questions;
while in both 5:2 & 6 'ayin expresses the absence of a savior (if Adonai can no longer be expected to perform this role).