"a regular door"
In the beginning lessons, they were just sounds, later we started getting words. An Arabic speaker on a discussion thread put together a list of all the words, phrases, and sentences in this course at: List of Words and Sentences in The Arabic course: up to the first checkpoint. forum.duolingo.com/comment/32975522
Is the pronunciation of the letter ع correct in the matching exercises where the letter ع is introduced? I've been listening to some YouTube videos where the sound of the letter is more harsh, more guttural. But, in our exercises it does not sound harsh or guttural at all. To me, it sounds wrong after listening to Arabic speakers on other sites.
UPDATE: Thanks TJ but I didn't mean the phrase on this page. I meant the matching exercises where ع was introduced, where the exercises look like this: برُع tirru3 ترُّع jayyid sammad جمَّع tiru3 جيِّد سَمَّد jamma3
The one you're hearing here in the word (عادي) is indeed the normal sound of (ع) [Ayn] - I think it's called pharyngeal sound. Not glottal.
The glottal sound which some people mix it up with (ع) is actually the Hamza character (ء) - they are totally different characters. Hamza is indeed a glottal stop.
Some resources, when teaching foreigners the Arabic alphabet, decide to choose the easy way out and make it easier for non-Arabs to say the letter [Ayn] by approximating it to Alif (i.e. glottal stop). To make it easier for them to pronounce. Same thing with the eltter (ح) which is a hard voiced fricative, which some approximate to "H" - or maybe Kh (German CH).
Here in this sentence it's -un (called Tanwin or Nunation).
Tanwin can be considered (at this level) as the marker for indefinite article, almost similar to a/an in English which comes before an unidentified word. I don't know why Duolingo is not using the diacritic for Tanwin here but here it should be like this:
I hope it's clear enough. The sign above is for (-un). Tanwin can come in various flavors: -un, -an, and -in, depending on the word's position in the sentence (Accusative, genitive...etc).
Just to complete the sentence above:
the last vowel on the last letter at the end of the sentence can be dropped because there is no word after that to bridge and it's ok to drop it.
In Br English, it would be normal/ordinary/standard. See this link, where the US sense of "regular" is the 7th definition; https://www.collinsdictionary.com/dictionary/english/regular
Away from the English translation of the word عادي (3ádiy) I have to say though that the meaning of this word has changed over time from the classical times into the modern times. And while people now use it to convey the meaning of: normal/regular/natural; I have to say that this is not the exact meaning (and many scholars pointed out and tried to fix the public usage of this word but without any success).
The original meaning of this word is "ancient" or "very old". This is because this word is an adjective derived from the name عاد (3ád), which is a very ancient Arabian tribe said to be closer in the timeline to the time of Noah (so we are speaking of thousands and thousands of years ago). If you are familiar with the stories of Quran you would have probably encountered the name and their story with their prophet Húd هود (and typically with their successors, the tribe of þamúd, and their prophet Sálih صالح). Arabs kept oral traditions for many of these past stories and thus such adjective did exist for that purpose to note something ancient.
Just a side note, Arabs typically divided the tribes of Arabia into 3 main categories: The Wandering Arabs العرب العاربة (al-3arab al-3áribah), The Arabized Arabs العرب المستعربة (al-3arab al-musta3ribah), and The Extinct Arabs العرب البائدة (al-3arab al-bá2idah); The tribes of Aad (3ád عاد) and Thamud (þamúd ثمود) belong to the last category: The Extinct Arabs.