Dictionary and Thesaurus.
Get a developer API key from here: http://www.dictionaryapi.com
example of a request to the Thesaurus API
curl http://www.dictionaryapi.com/api/v1/references/thesaurus/xml/cheese?key=ee2466d2-07a0-40af-b959-abcdeb125f0ca
Here’s the XML response – filled with synonyms:
<?xml version="1.0" encoding="utf-8" ?> <entry_list version="1.0"> <entry id="cheese"><term><hw>cheese</hw></term><fl>noun</fl><sens><mc>that which is of low quality or worth</mc><vi>you wouldn't believe the <it>cheese</it> that the movie studio puts out</vi><syn>cheese, crapola [<it>slang</it>], dreck (<it>also</it> drek), muck, rubbish, sleaze, slop, slush, trash, tripe</syn><rel>camp, kitsch; claptrap, humbug, nonsense; bomb, clinker, clunker, dud, lemon, stinker, turkey; mess, muddle, shambles</rel></sens></entry> <entry id="big cheese"><term><hw>big cheese</hw></term><fl>noun</fl><sens><mc>one of high position or importance within a group</mc><vi>thinks he's a <it>big cheese</it> just because he's got a business card</vi><syn>big, big boy, big cheese, bigfoot, biggie, big gun, big leaguer, big-timer, big wheel, bigwig, fat cat, heavy, heavy hitter, heavyweight, high-muck-a-muck (<it>or</it> high-muckety-muck), honcho, kahuna, kingfish, kingpin, major leaguer, muckety-muck (<it>also</it> muck-a-muck <it>or</it> mucky-muck), nabob, nawab, nibs, nob [<it>chiefly British</it>], pooh-bah (<it>also</it> poo-bah), wheel</syn><rel>baron, czar (<it>also</it> tsar <it>or</it> tzar), king, lion, magnate, mogul, prince, tycoon; VIP</rel><near>inferior, subordinate, underling; mediocrity, obscurity</near><ant>lightweight, nobody, nonentity, nothing, shrimp, twerp, whippersnapper, zero, zilch</ant></sens></entry> </entry_list>