On BBC4 TV recently there was an interesting programme entitled Metamorphoses. It was about animals that change their shape and/or lifestyle dramatically in the course of their lives: caterpillars turning into butterflies, tadpoles becoming frogs, and so on.
Metamorphosis, the singular form of metamorphoses, is one of those classical-derived words in which English speakers may hesitate about stress placement. In LPD, following Daniel Jones’s EPD, I give the main pron ˌmetəˈmɔːfəsɪs, with a secondary pron ˌmetəmɔːˈfəʊsɪs. M-W Collegiate and K&K give just the first stressing, as does ODP, although the Concise Oxford gives both, as does the OED (2001, for BrE; just the first for AmE).
On the TV programme all the scientists who took part, with just a single exception, gave it antepenultimate stress.
So why do some Brits, at least, want to stress the penultimate? Mainly, no doubt, because of other scientific words in -osis such as psychosis, neurosis, osteoporosis, cirrhosis, symbiosis, meiosis, tuberculosis, osmosis, hypnosis, sclerosis, all of which have penultimate stress, -ˈəʊsɪs.
Those few who know Classical Greek will know the etymon μεταμόρφωσις metamórphōsis, and in English will know as usual to ignore the classical Greek accentuation in favour of the Latin stress rule. In the Greek spelling the omega (ω, ō) in the penultimate syllable shows that the vowel is long and therefore, by the Latin stress rule, stressed.
Classicists and grammarians, though, may know the word apodosis əˈpɒdəsɪs (Greek απόδοσις apódŏsis) ‘then-clause’, paired with protasis ‘if-clause’ and having an omicron (ο, ŏ) followed by a single consonant in the penultimate syllable, giving a Latin and English antepenultimate stress. But then they’ll also know apotheosis (Greek ἀποθέωσις apothéōsis), which has an omega and therefore penultimate stress like the scientific words. Nowadays those of us who do know it say əˌpɒθiːˈəʊsɪs; but apparently that was not always the case in Enɡlish.
Under -osis the OED comments “The older pronunciation of at least some of these words had the stress on the syllable preceding the suffix: see, e.g., the etymological note at apotheosis n.” Under apotheosis we read (OED of 1885) “The great majority of orthoepists, from Bailey and Johnson downward, give the first pronunciation [sc. æpəʊˈθiːəsɪs], but the second [sc. əˌpɒθiːˈəʊsɪs] is now more usual”.