There are 16 10-letter words that start with 'sea'.
| seabeaches | seaborgium | seafarings | 
| sealifting | seamanlike | seamanship | 
| seamlessly | seamstress | searchable | 
| searchless | seasonable | seasonably | 
| seasonally | seasonings | seasonless | 
| seastrands | ||
Note: These 16 10-letter words that start with 'sea' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with seas, seam, seaw, sear, seat, seal, seab, seaf, seac, seap, sead, seag, seah, sean, seaq.
4-letter words start with 'sea' (5)