There are 31 8-letter words that start with 'under'.
Note: These 31 8-letter words that start with 'under' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with unders, underc, underp, underb, underl, underw, underg, undert, undere, undera, underr, underf, underd, underh, underv, underu, underi, underm, undern, underj, underk.
7-letter words start with 'under' (2)