Words that can be spelled with an OE or just an E that mean the same
thing either way:

AMOEBA
AMOEBAE
AMOEBAN
AMOEBAS
AMOEBEAN
AMOEBIASES
AMOEBIASIS
AMOEBIC
AMOEBOCYTE
AMOEBOCYTES
AMOEBOID
APNOEA
APNOEAL
APNOEAS
APNOEIC
ASAFOETIDA
ASAFOETIDAS
AUTOECISM
AUTOECISMS
BARRICADOED
BARRICADOES
BASTINADOES
BIOCOENOSES
BIOCOENOSIS
CAMISADOES
CARBONADOES
COELIAC
COELOM
COELOMATA
COELOMS
COENOBITE
COENOBITES
COURANTOES
DIARRHOEA
DIARRHOEAS
DIOECIOUS
DYSPNOEA
DYSPNOEAS
ENDAMOEBA
ENDAMOEBAE
ENDAMOEBAS
ENTAMOEBA
ENTAMOEBAE
ENTAMOEBAS
EUPNOEA
EUPNOEAS
EUPNOEIC
FOETAL
FOETID
FOETOR
FOETORS
FOETUS
FOETUSES
GAMBADOES
GYNOECIA
GYNOECIUM
HOLLOOED
MESOGLOEA
MESOGLOEAS
MONOECIOUS
OECOLOGIES
OECOLOGY
OECUMENICAL
OEDEMA
OEDEMAS
OEDEMATA
OENOLOGIES
OENOLOGY
OESOPHAGI
OESOPHAGUS
OESTRIN
OESTRINS
OESTRIOL
OESTRIOLS
OESTRONE
OESTRONES
OESTROUS
OESTRUM
OESTRUMS
OESTRUS
OESTRUSES
PHARMACOPOEIA
PHARMACOPOEIAL
PHARMACOPOEIAS
PHOENIX
PHOENIXES
SUBPOENA
SUBPOENAED
SUBPOENAING
SUBPOENAS
SYNALOEPHA
SYNALOEPHAS
ZOOECIA
ZOOECIUM
ZOOGLOEA
ZOOGLOEAE
ZOOGLOEAS

Words that are still good if OE is replaced with E but which then mean
something different:

ALOE
ALOES
BRAVOED
BRAVOES
BUNKOED
CALICOES
CANOE
CANOED
CANOES
CONGOES
COOED
CRAMBOES
CRUSADOES
DINGOES
DISCOED
DOE
DOMINOES
ECHOED
ECHOES
FICOES
FORGOER
FORGOERS
FORGOES
HALLOOED
HALOED
HALOES
HELLOED
HEROES
HILLOED
HOE
HOER
HOERS
HOES
HULLOED
HYPOED
IMAGOES
IMPASTOED
LASSOES
LOESS
MANGOES
MANIFESTOED
MOTTOES
OBOE
OBOES
OES
PALMETTOES
PASSADOES
PEKOE
PEKOES
POET
POETS
REDOES
RENEGADOES
RESHOES
ROE
ROES
SALVOED
SALVOES
SHAKOES
SHOE
SHOED
SHOES
SHOOED
SNOWSHOED
SOEVER
SOLOED
TANGOED
TOEA
TOED
TOENAIL
TOENAILS
UNDOER
WHOSOEVER
WINOES
WOE
ZOEAL