The online Arabic-English dictionary that reminds me most of the site you mentioned is PONS. It isn't exclusively an Arabic-English dictionary. Other language pairings are offered as well. To give you a taste of what it can offer, click on the link below:
You may also like WordReference.com. Here's what it does with this same word:
This (History SE) answer claims that the term was first used by Bishara Zalzal in an article in Al-muktataf magazine (here is a link indicating that the article exists). The report is that
I used al-batriq as the Arabic name for this bird because in Latin it
is named penguin which means the "chubby bird" and batriq means the
same thing in Arabic
mawjūd is the passive participle of the verb wajada “to find”, so its literal meaning is “having been found”. As a participle it is common in classical Arabic, but as far as I can see, in the meaning “existing” it is modern, or in case not common in the classical language. It might help if you could direct us to the mentioned link.
It is a word in both modern standard Arabic and classical Arabic. Just because it was not mentioned in the Qur'án does not mean it is not a word. The Qur'án is not a dictionary, and it does not have every word in the Arabic language. Further proof of it being a word is the fact that other words of the same root are indeed found in the Qur'án, it is just that ...