NYCHTHEMERAL
NYCHTHEMERON
NYCHTHEMERONS
NYCTAGINACEOUS
NYCTALOPES
NYCTALOPIA
NYCTALOPIAS
NYCTALOPIC
NYCTALOPS
NYCTANTHOUS
NYCTINASTIC
NYCTINASTIES
NYCTINASTY
NYCTITROPIC
NYCTITROPISM
NYCTITROPISMS
NYCTOPHOBIA
NYCTOPHOBIAS
NYCTOPHOBIC

19 words start with NYC.