glass, mass, bass, grass, brass, bliss, hiss, less, guess, press, mess, brass, toffee, coffee, butt, floss, moss,
addassallillofferrbeeseefeepeeteeweezooboocoogoomootoooddebb
buffcuffmuffpuffballbellbillbullcallcellmallmillmullnullpillpullrollsillselltilltelltallwallwellwillbassbosscussfusshisskisslessmessmissmassmosslosspasssasstossmuttmittbuttdollfallfellfillfull
Eel
There are no single English 6-letter words that end with FRO.
Ill and inn.
sully, sunny
Some six letter words that end in double letters:accessacrossapogeebamboobefallboo booboohoobungeebypasscaresscoffeecouleecuckoodecreedegreeduressegressembossenrollentreeexcessgoateeharassHawaiilayofflycheemorassmuumuupayoffpeeweepizazzrebuffrecallrecessrefillremissripoffrunoffscrollscruffsetteeshrillsoireesquallstressstrolltarifftattoothrilltoffeetoupeeunlessvoodoo
impress mastiff regress
abbreviationaccumulationaccentuationaggressivelyappreciationappropriatedconnotationsdissatisfieddisassociateexpressivelyinstallation
they are words that have two sounds to them
accessoryaddressaggressiveannuallyappallassessassassinbitternessbuccaneerblurrinessbulletproofbutterballbuttresscassettecarelessnesscarryallcoffeecommissarycommissioncrabbinessfurrinesshappinesspennilesspuffinessruddinesssluggishnessstiffnessstillnessstubbornnessstuffinesssuccesstallnessvolleyballwellnesswheelbarrow
Aardvark and eel are words. They begin with double letters.