There are 13 words that start with 'math'.
| math | maths | 
| mathematic | mathematics | 
| mathematize | mathematical | 
| mathematized | mathematizes | 
| mathematician | mathematizing | 
| mathematically | mathematicians | 
| mathematization | |
Note: These 13 words that start with 'math' are found from the USA & Canada version of the tournament Scrabble word list.