A palindrome is a word, phrase, number or other sequence of units that can be read the same way in either direction. Composing literature in palindromes is an example of constrained writing. The word "palindrome" was coined from Greek roots palin (πάλιν; "again") anddromos (δρóμος; "way, direction") by English writer Ben Jonson in the 17th century. The actual Greek phrase to describe the phenomenon is karkinikê epigrafê (καρκινικὴ επιγραφή; crab inscription), or simply karkinoi (καρκίνοι; crabs), alluding to the backward movement of crabs, like an inscription that can be read backwards.
Ambigrams have also been called 'vertical palindromes'
The most familiar palindromes, in English at least, are character-by-character: The written characters read the same backwards as forwards. Some examples of common palindromic words: civic, radar, level, rotor, kayak, reviver, racecar, and redder.
The longest palindromic word in the Oxford English Dictionary is the onomatopoeic tattarrattat for a knock on the door.
A few examples of palindromes that seem to make the most sense...
peeweep- a type of bird, often understood to be a lapwing
Semordnilap is a name coined for a word or phrase that spells a different word or phrase backwards. "Semordnilap" is itself "palindromes" spelled backwards.
stressed / desserts
rewarder / redrawer
departer / retraped
reporter / retroper
was / saw
gateman / nametag
deliver / reviled
straw / warts
star / rats
lived / devil
smart / trams
spit / tips
stop / pots
An ambigram is a typographical design or artform 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. Douglas R. Hofstadter describes an ambigram as a "calligraphic design that manages to squeeze two different readings into the selfsame set of curves." Different ambigram artists (sometimes called ambigramists) may create completely different ambigrams from the same word or words, differing in both style and form.
Ambigrams are exercises in graphic design that play with optical illusions, symmetry and visual perception. Some ambigrams feature a relationship between their form and their content. Ambigrams usually fall into one of several categories:
Rotational Through rotation, normally 180 degrees but sometimes 45 or 90. They can also form different words from the original, e.g. up and dn (abbreviation for down) or swoop and dooms.
Mirror-image...or glass door ambigrams, because they can be read from either side.