pneum-

Partly from erroneous abbreviation of the fuller forms within English, and partly from the Koine and Byzantine Greek πνεῠμο- (pneumo-), a rare combining form of both the Ancient Greek πνεῠ́μων (pneúmōn, “lung”) and the Ancient Greek πνεῦμᾰ (pneûma, “air”, “wind”, “breath”, “spirit”); compare the French, German, and post-Classical Latin pneumo- ⁽ᶠʳ⁾ ⁽ᵈᵉ⁾ ⁽ˡᵃ⁾.

• (Received Pronunciation) enPR: nyo͞om-, IPA^(key): /njuːm-/
• (General American) enPR: no͞om-, IPA^(key): /num-/

pneum-

1. Abbreviated form of pneumon-
2. Abbreviated form of pneumat-

• When combined with a word or another affix which begins with a consonant, this prefix concatenates with -o- (as pneumo-).

• “Pneumo-” listed on page 1,033 of volume 7 (O–P) of A New English Dictionary on Historical Principles [1ˢᵗ Ed.; 1909]
    Pneumo- (pniūmo-, niū-), combining form and verbal element, a. Gr. πνεῦμα wind, spirit, etc. (see Pneuma), = the fuller form Pneumato- (cf. Gr. αἱμο- = αἱματο-, etc.), in various scientific terms. b. Short for pneumono-, f. Gr. πνεύμων, -μον-, lung; chiefly in terms of pathology, most of which occur also in the fuller form Pneumono-.
• “pneumo-” listed in the Oxford English Dictionary [2ⁿᵈ Ed.; 1989]
    /pnjuːməʊ-, njuː-/
• “pneumo-, comb. form” listed in the Oxford English Dictionary [draft revision; Mar. 2010]
    Apparently partly from Hellenistic and Byzantine Greek πνευμο-, rare combining form of both ancient Greek πνεῦμα and πνεύμων[.]