This is monolingual mode is a great addition. I am new to the site. If it has not been suggested, for learners of American English, there's http://learnerdictionary.com and Longman and Cambridge both have good British English online dictionaries for learners.

Whoa! About time, now I have a use for this and will check it out!!

@oliverrose If I did go ahead with a more integrated monolingual dictionary, do you think Wiktionary (http://en.wiktionary.org/wiki/Wiktionary:Main_Page) would be a good choice?

(Note that to make use of the raw data from a dictionary it will need to be released under a suitable copyright license such as some of the Creative Commons ones.)

Even if supporting all languages is not possible, it would be very desirable just in those main ones for which dictionaries are available, such as English.

@Aron Thanks for the links, those dictionaries could be handy for people wanting to customise their dictionary as explained here:

http://blog.readlang.com/2013/11/07/custom-dictionaries.html

Unfortunately, most online dictionaries don't allow other services like mine to make use of their data. I can only present it in the form it appears on their website, so I couldn't extract just the text of the definition to insert in the text like I do with the Google Translate translations for example. To properly integrate monolingual dictionaries I need a database of translations without restrictive copyright.

Wiktionary, which has a Creative Commons licence, could be a good option to consider in future.

Indeed a good idea. I voted it up. Here is a monolingual Spanish dictionary: http://lema.rae.es/drae/

Benny gathered many dictionary links on this page: http://www.fluentin3months.com/free-dictionaries/

Also, with an advanced grasp of a language, it quickly becomes evident that the direct translations provided from google are insufficient whereas a monolingual definition is easily understand and more comprehensive for learners at this level.