FOCI is a playable word

focus Scrabble® Dictionary

noun
pl. focuses or foci
a point at which rays converge or from which they diverge
verb
focused, focusing, focuses or focussed, focussing, focusses
to bring to a focus
6 Playable Words can be made from "FOCI"
   2-Letter Words (3 found)
   4-Letter Words (3 found)