The spelling of the word "sullener" is derived from the root word "sullen". The IPA phonetic transcription for "sullener" is /ˈsʌl.ən.ər/. The -er suffix indicates that this word is describing a person who is sullen, moody or sulky. The double "l" in "sullen" is retained in "sullener" to indicate that the word is derived from its base form. The -en- infix is used to form a comparative adjective, with "sullener" meaning more sullen than another person.