Perhaps the broadest of all the Oxford English Dictionary's entries for "monster" is, "something extraordinary or unnatural." This seems to cover most of the uses of "monster" throughout "Othello." However, the word is still used in many different ways. The connotation of the word depends upon the tone of the scene. For example, in the beginning, before any real drama develops, "monstrous" is used only to describe the tempestuousness of the sea. However, later, as the plot thickens and problems develop, the word monster begins to describe horrible acts or people. A number of times, Othello is referenced as a monster by both others and himself. As so much of the plot revolves around Othello's insecurities, the word "monster" and its definition becomes key as it reiterates just how "unnatural" Othello is.
Barbarian is also used by Iago to describe Othello. A barbarian is defined as both a foreigner and as an uncultured or uncivilized person. A double meaning is present here in Iago's words since both of these definitions apply to Othello. He is clearly marked as an outsider amongst the Venetians and, unfortunately because he is not a part of their society they see him as an unrefined and uncultured individual. This is, again, a very aptly chosen word as it makes reference to the driving force behind this play's twisted plot: Othello's insecurity.
Also, the speaker of these words seems to vary with the different times of the play. One finds that, in the beginning of the play, if the words "monster" or "barbarian" were to be used as an insult to