The given quote "maybe the two different worlds we lived in were not so different. We saw the same sunset" can be found on Page 40 in the book "The Outsiders" by S.E. Hinton.
the page number may differ considering the publication and version one is using.
The synonym of a word is a word with the same meaning. Effrontery means acting in a rude way, thus arrogance has the closest definition to effrontery and is the synonym.