sillyoudaoicibaDictYouDict[sill 词源字典]
sill: [OE] Sill originally denoted the ‘foundation of a wall’. Not until the 15th century was it used for the ‘base of a window-frame’. It is related to German schwelle ‘threshold’ and possibly also to English sole ‘underside of the foot’.
[sill etymology, sill origin, 英语词源]
sill (n.)youdaoicibaDictYouDict
Old English syll "beam, threshold, large timber serving as a foundation of a wall," from Proto-Germanic *suljo (cognates: Old Norse svill, Swedish syll, Danish syld "framework of a building," Middle Low German sull, Old High German swelli, German Schwelle "sill"), perhaps from PIE root *swel- (3) "post, board" (cognates: Greek selma "beam"). Meaning "lower horizontal part of a window opening" is recorded from early 15c.