Although I read Dan Brown’s Angels and Demons (2000), I don’t recall having noticed the word ambigram. When I watched the film based on the book, however, I did notice it, and found myself becoming vaguely annoyed by the frequency with which Tom Hanks says it. I thought he was intending to say “anagram”:
anagram: transposition of letters in a word so as to form another
My usual starting places when I want to write about words– the OED, Merriam-Webster, and the OnlineEtymologyDictionary–are all silent on ambigram, but here’s a definition from Wikipedia:
An ambigram is a typographical design or artform [sic] that may be read as one or more words not only in its form as presented, but also from another viewpoint, direction, or orientation. The words readable in the other viewpoint, direction or orientation may be the same or different from the original words.
Although not yet in the big dictionaries, ambigram is in common use by tattoo enthusiasts and others. There’s even a magazine dedicated to this type of ambiguous design: Ambigram Magazine.
The word combines Latin ambiguus, “having double meaning, shifting, changeable, doubtful,” with gram, which is derived from Greek graphein, “to draw, write.”
The word is of recent coinage. According to the Wikipedia article, it originated with Indiana professor Douglas Hofstadter and his friends in the early 1980s. Two graphic designers associated with this type of drawing are John Langdon and Scott Kim.
Other readers of Angels and Demons were more attentive than I was. The book is credited with popularizing both the word and the type of drawing that it denotes.