There are 15 words that start with 'posth'.
| postheat | posthole | 
| posthaste | postheats | 
| postholes | posthastes | 
| posthumous | postharvest | 
| postholiday | posthospital | 
| posthumously | posthypnotic | 
| postholocaust | posthumousness | 
| posthemorrhagic | |
Note: These 15 words that start with 'posth' are found from the USA & Canada version of the tournament Scrabble word list.