A translation service is not being requested in the question since they provide word-to-word mappings instead of word-to-meaning explanations. The dictionary may optionally render the Greek word with the Roman alphabet but must include one or more definitions in English that explain the meaning. In particular, I am trying to find out why "εκκλησάκι" and "παρεκκλήσι" are translated the same into English and hoping to read a full explanation of how they are different.
I usually use different dictionaries when I want to know the intricacies of a word, as I have not yet found a perfect one.
My first stop is usually on Wiktionary. The Greek one has much more entries than the English one (for Greek words) but a lot of them lacks definitions or are just declination of a lemma.
I'll sometimes take a look at Wordreference.com, but I'm not sure if the entries are manually created by someone or if they are taken from another website.
There's also this Greek only dictionary which I find quite professional.
Also take a look at this question on Language Learning SE.
I don't know what your level is but it will surely improve if you try to read definitions in Greek, even if you don't understand them very well at the beginning.
You can also look at one of the most complete (if not the most) Ancient Greek-English dictionary, available online here. This may help you understand etymologies of Modern Greek words.
Unless someone has found the definite Greek-English dictionary, looking at the etymology of the word might help you greatly. For example,
- εκκλησάκι literally means "small church", from εκκλησία + -άκι (diminutive suffix)
- παρεκκλήσι, literally means "next to, near the church", from παρα- + εκκλησία
I'm not a native speaker but my guess is that the first word can be used for any church that is small in size, while the second word is for a (small) church that belongs or depends from another one.
In the Greek only dictionary I mentioned above εκκλησάκι, εκκλησούλα and εκκλησίτσα are all listed as diminutives under the εκκλησία entry while παρεκκλήσι has its own definition:
μικρή εκκλησία που ανήκει σε κάποιο ίδρυμα, σε κπ. ιδιώτη ή που εξαρτιέται από άλλη μεγαλύτερη
small church which belongs some institute or private individual, or that depends from another bigger one
(PS, I also have a written dictionary but it's not in English...)