This particular dictionary's [legal notice][1] says that:

> Users are not entitled to [...] transmit [..] it on any other website without the express permission of Pearson.

> You must not use data mining, robots, scraping or similar data gathering or extraction methods on **any part of** this Site without our express prior written consent *(my emphasis)*

So either contact them, or use a more open dictionary.  
See this list of [open English dictionaries][2].

  [1]: http://uk.pearson.com/legal-notice
  [2]: http://opendata.stackexchange.com/questions/4341/free-english-dictionary