Excommunicate is a 13 letter word. It begins and ends with the letter e.
Boardinghouse and brainstorming are 13 letter words. The 3rd letter is the letter a.
In the absence of a definition, I'll provide one. What is a 13 letter word for vertical? Answer: perpendicular
Some 13 letter words that start with the letter a:abbreviationsabnormalitiesacceptabilityaccessibilityaccommodationaccreditationacquaintancesacupuncturistadministratoradmissibilityadvertisementaffordabilityalgebraicallyalternativelyanniversariesannouncementsanticipationsapplicabilityappropriationapproximationarchitecturalassassinationassignabilityastonishinglyattainabilityattentivenessauthenticallyauthoritativeauthorization
Correspondent
perpendicular
encouragement
A 13-letter word that starts with "s" and ends with "s" is "schoolteachers."
quadrilateral
international
unimaginative
acceptabilityaccommodationadvertisementalternatively