Sentence:  I catch on your face the old sad smile / Of our ancient <WSD>disillusionment</WSD>, / When the ardent crowd tries to beguile / Your world-old soul to impassionment. 
Meaning of the word marked with <WSD> tags:  A feeling of disappointment, akin to depression, arising from the realization that something is not what it was expected or believed to be, possibly accompanied by philosophical angst from having one's beliefs challenged.