Ambiguity is the quality of having more than one meaning; does "A friend in need is a friend indeed" mean that a friend in your hour of need is truly a friend, or a friend who needs something will act in a friendlier fashion? William Empson managed to fill a book, Seven Types of Ambiguity, with an in-depth investigation of this topic.
Andrew Fusek Peters' 'Hey Diddle Diddle' delights in finding the ambiguity in phrases that familiarity has obscured.
How to use this term
Peter Dale's 'Window' uses "Reflections" in both its senses, images and thoughts, in the first line of the second stanza; the second line's ambiguous reference to 'mine' combines both meanings, neither of which will touch the child.