There are 16 8-letter words that start with 'mag'.
| magalogs | magazine | magdalen | magentas | 
| magician | magicked | magister | magmatic | 
| magnates | magnesia | magnesic | magnetic | 
| magneton | magnetos | magnific | magnolia | 
Note: These 16 8-letter words that start with 'mag' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with magn, magi, maga, magd, mage, magm, magg, magu, magl, mago, magp, mags.
4-letter words start with 'mag' (3)