From Ask Figaro:
In The Last Unicorn, Peter Beagle described the unicorn as having amarathine eyes. This uses both meanings of “amarathine” simultaneously (undying and a purple color) without it being a pun or zeugma. Is there a word for this literary device?
It is indeed a kind of pun called the antanaclasis (an-ta-NA-cla-sis), or double entendre. Not the joking, play-on-words kind of pun, the antanaclasis strikes a rhetorical chord, causing the word to vibrate with its double meaning — a bicorn, if you will.