When combined with a word or another affix which begins with a consonant, this prefix concatenates with -o- (as pneumato-).
This prefix is sometimes erroneously abbreviated to pneum-.
From πνεῠμᾰτ- (pneumat-), the stem of the Ancient Greek πνεῦμᾰ (pneuma, “air”, “wind”, “breath”, “spirit”); compare the Englishpneuma and pne-, as well as the French, German, and post-Classical Latinpneumato- ⁽ᶠʳ⁾ ⁽ᵈᵉ⁾ ⁽ˡᵃ⁾.
English Wiktionary. Available under CC-BY-SA license.