FEIGN
FEIGNED
FEIGNEDLY
FEIGNEDNESS
FEIGNEDNESSES
FEIGNER
FEIGNERS
FEIGNING
FEIGNINGLY
FEIGNINGS
FEIGNS
FEIJOA
FEIJOAS
FEINT
FEINTED
FEINTER
FEINTEST
FEINTING
FEINTS
FEIRIE
FEIS
FEISEANNA
FEIST
FEISTIER
FEISTIEST
FEISTILY
FEISTINESS
FEISTINESSES
FEISTS
FEISTY

30 words start with FEI.