Easton's Bible Dictionary (1897)
A highway; a twig, only in 2 Kings 12:20. If taken as a proper name (as in the LXX. and other versions), the locality is unknown.
Smith's Bible Dictionary (1863)
(a highway). “The house of Millo which goeth down to Silla” was the scene of the murder of King Joash. (2 Kings 12:20) What or where Sills was is entirely matter of conjecture. Some have suggested the pool of Siloam.
Hastings' Dictionary of the Bible (1898) & Schaff's Bible Dictionary
SIL'LA (a twig), a place near which King Joash was slain. 2 Kgs 12:20. It was evidently in the valley below Millo.
Hitchcock's Bible Names (1869)
exalting