Well, you got yourself in deep detailed area my friend ???? I'll try to simplify it to you as much as I could.. الزواج is a word coming from the source زوج which means "pair" so any two things that complete each other and when joined together make one "perfect" thing could be called زوج so that makes (الزواج) means something near: Marrying one's soul mate (marrying between a man and a woman who are the perfect couple for each other, which make them count as one perfect family) And as for النكاح is more near to mix two components together (mixing them doesn't necessarily mean they make the perfect outcome) with the possibility of them un-mix with time.النكاح is most likely to be said instead of الجماع (which means having sex) and that makes people mix the meanings and forget the real meaning of النكاح. Also when النكاح is used to mean having sex it's used to tell that that sex is between a married couple, but الجماع doesn't necessarily mean that it happened between "married" couple. If you go back to the Holy Qur'an you will find the best usage of الزواج and النكاح (also the best usage is in the Hadieth too). So you can now understand the Hadieth you mentioned as speaking of "only marriage" but not necessarily the perfect meaning of it which is included in الزواج word. I hope i helped you, and I hope I didn't bore you with all that explanation.

الزَّواج : الاِرْتِباطُ بامْرَأَةٍ اِرْتِباطاً شَرْعِيّاً حَسَبَ الأُصولِ http://www.almaany.com/ar/dict/ar-ar/%D8%A7%D9%84%D8%B2%D9%88%D8%A7%D8%AC/ معنى النكاح لغة وشرعا: http://islam4beauty.blogspot.com/2010/02/blog-post.html أخ أحمد، إذا أردت كتابة "جزاكم الله خيرًا" باللغة الإنجليزية، فأرجو تصحيحها إلى: Jazakum Allahu Khairan

الزواج :is a ward indicates to coupling or adhesion that involves no seperation. this word isnot only used for people it also used for inanimates ,plants and animals . it's not necessary to find نكاح in الزواج . here are some instances أَوْ يُزَوِّجُهُمْ ذُكْرَاناً وَإِنَاثاً وَيَجْعَلُ مَنْ يَشَاءُ عَقِيماً إِنَّهُ عَلِيمٌ قَدِيرٌ) (الشورى: 50) this mean that allah may give to someone a couple of male ,another may have a couple of female and the other have no child وَأَنزَلَ مِنَ السَّمَاءِ مَاءً فَأَخْرَجْنَا بِهِ أَزْوَاجاً مِّن نَّبَاتٍ شَتَّى) (طه53). here allah says that he get out from the ground lots of types of a couple of plants احشروا الذين ظلموا وأزواجهم) أي قرناءهم. here also ازواجهم means their partners so if the holy Quran use the ward 'الزواج' instead of 'النكاح ' that means that any man get married to any woman mustn't get a divorce or seperated .it also means that all the marraiges are ideal and that isn't true . there are lots of problems between married people ...so you will find in holy Quran that there are just 2 positions of the ward 'النكاح " in the meaning of marriage here you are (مُتَّكِئِينَ عَلَى سُرُرٍ مَّصْفُوفَةٍ وَزَوَّجْنَاهُم بِحُورٍ عِينٍ) (الطور20)، as there will be divorce here . it's an ideal marriage فَلَمَّا قَضَى زَيْدٌ مِّنْهَا وَطَراً زَوَّجْنَاكَهَا) (الأحزاب37)، and here because this marriage was between prophet( peace be upon him ) and Mrs zainab . . . . finally i hope you will understand me and i apologize if my english is very weak i am still learning

(يا أيها الذين آمنوا إذا نكحتم المؤمنات ثم طلقتموهن من قبل أن تمسوهن فما لكم عليهن من عدة تعتدونها) تمسوهن = sex ..............نكحتم = marriage contract

In Qur'an nikah (marriage contract)