ENOfficial
It was narrated that Sa'eed bin Al-Musayyab said: "Khamr is so called because it is left until the good parts are gone and the dregs remain." And he disliked everything that was made by using dregs (by adding new materials to the dregs).
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا سُوَيْدٌ، قَالَ أَنْبَأَنَا عَبْدُ اللَّهِ، عَنْ شُعْبَةَ، عَنْ قَتَادَةَ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، قَالَ إِنَّمَا سُمِّيَتِ الْخَمْرُ لأَنَّهَا تُرِكَتْ حَتَّى مَضَى صَفْوُهَا وَبَقِيَ كَدَرُهَا . وَكَانَ يَكْرَهُ كُلَّ شَىْءٍ يُنْبَذُ عَلَى عَكَرٍ .
sunnah.com