The quality or state of being ambiguous; doubtfulness or uncertainty, particularly as to the signification of language, arising from its admitting of more than one meaning; an equivocal word or expression.
For chain letters: contradictory statements and testimonials, or a lack of specificity, concerning what recipient behavior may or may not produce good or bad luck. For example, will merely passing on the received copy avoid bad luck? Must you meet the deadline to receive good luck for distributing copies? Also misleading details concerning the possible national or religious source of a chain letter. Might "Bishop Lawrence," a well known Episcopalian to Protestant readers in 1905, appear to be Catholic to Catholic readers [ US, 1905]? Ambiguity apparently increases propagation by accommodating multiple interpretations.