See also: 老窦
old; aged; venerable; outdated; experienced; (affectionate prefix)
hole; aperture; cavity; sinus (anatom.)
From 老頭／老头 (lou5 tau4), possibly due to dialectal (Shunde) influence. The choice of using 竇 may be influenced by the connection with Dou Yujun (竇禹鈞), father of five sons, who had the right method of teaching them.