sloeyoudaoicibaDictYouDict[sloe 词源字典]
sloe: [OE] Etymologically, the sloe is probably the ‘blue-black’ fruit. The word comes, along with its relatives German schlehe, Dutch slee, Swedish slå, and Danish slaa, from a prehistoric Germanic *slaikhwōn, which has been linked with Latin līvēre ‘be blue-black’ (source of English livid [17]). Another close relative is Serbo-Croat shljiva ‘plum’, whose derivative shljivovica ‘plum brandy’ has given English slivovitz [19].
=> livid, slivovitz[sloe etymology, sloe origin, 英语词源]
sloe (n.)youdaoicibaDictYouDict
fruit of the blackthorn, Old English slah (plural slan), from Proto-Germanic *slaikhwon (cognates: Middle Dutch sleeu, Dutch slee, Old High German sleha, German Schlehe), from PIE *sleie- "blue, bluish, blue-black" (see livid).

The vowel has been influenced by that in the old plural form, which according to OED persisted into the 17c. Scottish slae preserves the older vowel. Sloe-eyed is attested from 1804; sloe gin first recorded 1878.