documentclass{book}
usepackage[margin=0.5in, paperwidth=6in, paperheight=9in]{geometry}


 usepackage{times}
usepackage{polyglossia}
setmainlanguage[variant=ancient]{greek}

usepackage{makeidx}

 setromanfont{FreeSerif}
setsansfont{FreeSans}
setmonofont{FreeMono}
setmainfont{DejaVuSerif}

%
usepackage{chngcntr}
counterwithout{section}{chapter}

makeindex
begin{document}

renewcommandindexname{εὑρετήριον}
section{τὸ σῶμα}
begin{enumerate}
item  κεφαλή, ἡ index{κεφαλή, ἡ}
item σκέλος, εος, τό index{σκέλος, εος, τό}
end{enumerate}
section{τὸ γυμνάσιον}
begin{enumerate}
item  βάθρον, τό index{βάθρον, τό}
item συμμαθητής, οῦ, ὁ  index{συμμαθητής, οῦ, ὁ}
end{enumerate}
printindex

end{document}