IS
ISABEL
ISABELLA
ISABELLAS
ISABELLINE
ISABELLINES
ISABELS
ISAGOGE
ISAGOGES
ISAGOGIC
ISAGOGICS
ISALLOBAR
ISALLOBARIC
ISALLOBARS
ISAPOSTOLIC
ISARITHM
ISARITHMS
ISATIN
ISATINE
ISATINES
ISATINIC
ISATINS

22 words start with ISA.