See EmEditor Help – Dialog Boxes -Search Only Word check box: “A word is defined as a string that begins and ends with any of these characters: A – Z, a – z, 0 – 9, or an underscore.”

To do what you want you can use regular expression: bιb
b matches word boundary

In JavaScript:
document.selection.Replace(“bιb””,””,eeFindNext | eeFindReplaceCase | eeReplaceAll | eeFindReplaceRegExp);