knowing this, « ĂȘtre » becomes much more regular :
ĂȘtreâââ estreâ(es, est, sommes, ĂȘ[s]tes, sont ; ser-)
some French derivations become clearer :
fenĂȘtre  â dĂ©fenestrerââ L. fenestra
hĂŽpitalââ hospitaliserâ(E. hospital, ise)
intĂ©rĂȘt ââ intĂ©ressantâ(E. interest, -ing)
ancĂȘtre â ancestralâ(E. ancestor, -ral)
arrĂȘt â â arrestation
Ă©pĂźtreâ â Ă©pistolaireâ(E. epistle)
some English cognates become more obvious :
hĂŽtelâ â hostelâ(E. âhotelâ borrowed from French)
forĂȘtâ â forestâ(tipp to remember ^ goes on the âčeâș)
pĂąte, pĂątĂ© â pasta, paste
vĂȘtements â vestments (ie. clothes)
sometimes, the acute replaces the circumfex for phonetic reasons :
ážcoleââ â escoleââ L. schola (E. school)
ážtranger  â estrangierâ(E. stranger)
ážtudier â â estudierâ(E. study)
dážgoĂ»tant â desgoustantâ(E. disgusting)
dážbarquer â desembarquerâ(E. disembark)
rážpondre â respondreâ(E. respond)
rážpublique â L. res publica
Also, where « c â ch » (eg. cantareâ chanter) :
chĂąteau â castelâ(E. castle)
and « w â gu » (eg. warâ guerre ; wardenâ guardian) :
guĂȘpe â E. wasp !â(this is my n° 1 favourite cognate)
fantĂŽme â L. phantasmaâ(E. âphantomâ borrowed from French)
PĂąques â Gk. pĂĄsxa â Am. pĂ©saáž«â(E. Paschal)
Also just be aware that the circumflex has some other uses too, like distinguishing « sur â sĂ»r » or « dĂ» » and the vowel quality in « Ăąge »