Not to dwell on arabic, but in fact formal arabic is rarely spoken, and 99% of Arabs actually commonly speak a dialect that can vary greatly between arab countries and even within, depending on origin.
What Hugeschlongedteen explained is correct, but to my knowledge is more Persian Gulf arabic (where I lived for 15 years but still can barely speak or understand) or even possibly Egyptian. I'm Middle Eastern, so as a Lebanese I would be more inclined to say "zib" for cock, or more vulgar "ayr".
"Kbeyr" - dialect for "Kabeer" would still be correct for big and most common to me, not so much "khadm" - formal arabic for fat or very thick, or "jabbar", formal arabic again, which refers usually to strength and more acuratly translates to mighty (in fact for Muslims it is one of God's - or Allah's - names). "tcheen" (ch = a guteral throat scratching sound that Germans and Israelis are most known for) would be runner up and mean thick.
In short, in Lebanese I'd say "zib kbeer" or "zib tcheen" talking about one, OR if adressing the guy, "zibak/ayrak kbeer/tcheen", OR if said in exclamation/awe "yahy shoo kbeer/tcheen (ziback/ayrak could be left off if you are staring at it)".
And I have no clue what Northern African Arabs would say (excluding Egypt), and I'm imagining Iraqis would be closer to middle-eastern but still different. Syrian and Lebanese vary only slightly, Palestinian is most different of the Middle Eastern dialects, and Jordanian has aways sounded more formal in a way, and possibly closer to what Hugeschlongedteen was explaining.
Just goes to prove that Arabic is VERY different and complex.
Actually, rom, in Arabic, الديك (al-Deek) means 'the cock', but in the sense of a rooster, not a penis.
As far as I know, قضيب (khadheeb) is the closest that you're going to get to cock. It means a lot of different things, like bar and staff and shaft, but it is also used in slang to mean prick or dick or penis. There is also زبر (zubr), which also means penis. More comically (most Arabs actually do have a great sense of humor) الة الرجل (ilah al-rajl) is sometimes used to mean penis, which is funny because, literally, this is 'the god of man'. I'm sure that some women (and men) might agree with that assessment.
As far as size goes, you can go with كبير (kabir) 'big', خضم (ckudhum) 'huge', or جبار (jabar) 'enormous, colossal', depending on how big you're talking about. I'd definitely be flattered if someone used the latter to describe mine.
Long story short, قضيب كبير (khadheeb kabir) would be a decent translation for 'big cock' in Arabic.
We should probably add "огромный" too, as in огромный хуй (pron. uh-GROHM-ny khuy**), or "huge/enormous cock".I am a Russian an I would like to correct the previous proposals for translation to my language.
In Russian 'cock' is хуй. Spelling is 'khuy'. Literary translation of 'Big cock' is 'большой хуй' or 'bol'shoy khuy'.
In one word it is often used as 'хуище', spelling is 'khuische'.
N.B. Previous proposal "khuylo" is totally wrong. In Russian it means "very unpleasant person" and has nothing in common with the member of the body.
Try to pronounce .....