First, be aware that manoeuvre is now normally spelled maneuver in America, and indeed, has fallen behind maneuvre in England. Even the Economist (but not the Œconomist :) uses maneuvre now.
Rendering Typographic Ligatures Correctly
The general answer is that œ is considered a mere typographic ligature in written English, not a lexical ligature as it is in French. See this answer for more about all that.
It is the modern custom to print all instances of œ as oe in English. Indeed, the OED switched its custom from the ligated digraph to the separated form when it went from its 2nd to its 3rd edition.
Therefore, for example, these words are all now typically printed differently. Notice how in some instances, the oe reduces to e. Although increasingly common, that reduction is by no means universal, and does not occur in all words, either.
- amœbæ > amoebae
- apnœa > apnoea, apnea
- cœlacanth > coelacanth
- diarrhœa > diarrhoea, diarrhea
- homœopathic > homoeopathic, homeopathic
- manœuvre > manoeuvre, maneuvre, maneuver
- melopœïa > melopoeia
- Mœbius > Moebius, Möbius, Mobius
- œdema > oedema, edema
- Œdipus > Oedipus
- œnologist > oenologist
- epopœia > epopoeia
- œsophageal > oesophageal, esophageal
- œstrous > oestrus, estrus
- Phœbus Apollo > Phoebus Apollo
- Phœnician > Phoenician
- phœnix > phoenix
- subpœna > subpoena
Two Exceptions: Lexical Ligatures and the IPA
There are two important exceptions to this.
The first is in terms taken from the French and considered “unassimilated” into English. These are typically set in italic. Since œ is a lexical not a typographic ligature in French, when printing French terms it is imprescindible that the ligature be maintained. For example:
- à contre-cœur
- casus fœderis
- chef d’œuvre
- cri de cœur
- hors d’œuvre
- œuf en cocotte
- œufs sur le plat
- vœu, vœux
Whether to preserve it in Latin terms like casus fœderis or subpœna is more controversial. Usually, it is not.
The other important exception is when printing phonetic or phonemic transcriptions in the International Phonetic Alphabet (IPA). There are two glyphs that mean something special in IPA, and which must be preserved:
The relevant code points in Unicode are:
Œ 0152 LATIN CAPITAL LIGATURE OE
œ 0153 LATIN SMALL LIGATURE OE
= ethel (from Old English eðel)
* French, IPA, Old Icelandic, Old English, ...
x (latin small letter ae - 00E6)
x (latin letter small capital oe - 0276)
ɶ 0276 LATIN LETTER SMALL CAPITAL OE
* low front rounded vowel
x (latin small ligature oe - 0153)
Note that these are the only code points whose names include the word LIGATURE but which are generally considered lexical not typographical ones. Unlike the others with LIGATURE in their names, these have no decomposed forms that produce two glyphs, nor are they casewise equivalent to the two-glyph version they are currently spelled with in most English words. This is because you would get the wrong results under certain conditions if you did so.
These are the other Latin ligatures in Unicode; all are considered typographic in most languages, and have special decomposition and casing rules:
Ĳ 0132 LATIN CAPITAL LIGATURE IJ
# 0049 004A
ĳ 0133 LATIN SMALL LIGATURE IJ
# 0069 006A
ﬀ FB00 LATIN SMALL LIGATURE FF
# 0066 0066
ﬁ FB01 LATIN SMALL LIGATURE FI
# 0066 0069
ﬂ FB02 LATIN SMALL LIGATURE FL
# 0066 006C
ﬃ FB03 LATIN SMALL LIGATURE FFI
# 0066 0066 0069
ﬄ FB04 LATIN SMALL LIGATURE FFL
# 0066 0066 006C
ﬅ FB05 LATIN SMALL LIGATURE LONG S T
# 017F 0074
ﬆ FB06 LATIN SMALL LIGATURE ST
# 0073 0074
Note that all of those are there for legacy round-tripping, and no more such things shall ever be added to Unicode. That is because unlike lexical ligatures, typographic ligatures belong in the font, not the code points.
That is why the typographical ligatures given above get split up under decomposition and caseless matching, but the lexical ligatures do not.
The exception to this is when using the (default, untailored) Unicode Collation Algorithm (UCA) for sorting. Now these code points sort next to the two-glyph version, and count as equivalent at the primary strength (that is, whether they are the same letters or different ones, and without regard to case or diacritics).
Here then is the result of sorting the various words pointed out above using the default UCA:
à contre-cœur, amoebae, amœbæ, apnea, apnoea, apnœa, bœuf, casus fœderis,
chef d’œuvre, coelacanth, cœlacanth, cri de cœur, diarrhea, diarrhoea,
diarrhœa, edema, epopoeia, epopœia, esophageal, estrus, homeopathic,
homoeopathic, homœopathic, hors d’œuvre, maneuver, maneuvre, manoeuvre,
manœuvre, melopoeia, melopœïa, Mobius, Möbius, Moebius, Mœbius, mœurs,
oedema, œdema, Oedipus, Œdipus, œil-de-bœuf, oenologist, œnologist,
oesophageal, œsophageal, œstrous, oestrus, œuf en cocotte, œufs sur le
plat, œuvre, Phoebus Apollo, Phœbus Apollo, Phoenician, Phœnician, phoenix,
phœnix, subpoena, subpœna, vœu, vœux.