"meekly as a maid..."
See in text (The General Prologue - The Knight)
Here, maid means both young woman and also a young man with the composure to remain chaste. Chaucer uses this simile to show both the Knight’s character and continue to demonstrate his adherence to his chivalric vows. In using this simile to compare the Knight to a chaste man he becomes as meek, or gentle and courteous, as the chaste man, both qualities that are important to the chivalric code.
"as loud as does the chapel bell..."
See in text (The General Prologue - The Monk)
This simile compares the bells on the monk's bridle to the bells in a church in order to suggest that they are of equal importance to the Monk. Notice that the description of the Monk's riding gear gets three lines here while the church only gets one. This could suggest that the Monk's riding is more important to him than his calling.
"he was like a lord or like a pope...."
See in text (The General Prologue - The Friar)
This simile compares the poor ragged clothing of a cloistered monk to the rich attire of the pope or an aristocrat. It demonstrates that the Friar dresses well. Since the cloistered monk is his point of comparison for poor clothing, the comparison also suggests that the Monk who was [previously described] (http://www.owleyes.org/read/canterbury-tales/the-monk#root-218780-1) did not stand for all monks.
"as two boars ..."
See in text (The Knight’s Tale)
Notice that the two knights keep being referred to as animals, rather than men. This simile emphasizes the loss of their chivalric qualities and suggests that their love for Emily has removed their humanity.