伍つ[itsutsu] five
伍長[gochou] corporal
卒伍[sotsugo] rank and file
落伍[rakugo] dropping out of
落伍者[rakugosha] dropout

隊伍[taigo] ranks of troops
伍を重ねる[gowokasaneru] to double the ranks
先頭伍[sentougo] leading file
伍する[gosuru] to rank with