Nguyễn Kim
Based on Chinese observers' remarks that the "Lạc" people's paddies depended on water-control systems like tidal-irrigation &amp; draining, so that the floody, swampy Red River delta might be suitable for agriculture, many scholars opted to find its etymology in the semantic field "water". Japanese scholar Gotō Kimpei links "Lạc" to Vietnamese noun(s) "lạch" ~ "rạch" "ditch, canal, waterway". Vietnamese scholar Vũ Thế Ngọc cites Nguyễn Kim Thản's opinion that "Lạc" simply means "water" and is comparable to phonetically similar elements in two compounds "nước rạc (lit. "ebbing (tidal) water") &amp; "cạn rặc (lit. "utterly dried up [of water]")