Herbert Weir Smyth, A Greek Grammar for Colleges

SHORTENING, ADDITION, AND OTHER VOWEL CHANGES

[*] 39 D. In the Ionic genitive of  stems (214 D. 8) -εων is from -ηων out of -α_ων. So in Ionic βασιλέα from βασιλῆα king. So even before a short vowel in Hom. ἥρω^ος, ἥρω^ι hero (cp. 148 D. 3).

[*] 40. A long vowel before ι, υ, a nasal, or a liquid + a following consonant was regularly shortened: να^ῦς from original να_υς ship, ἐμίγεν from ἐ-μιγη-ντ were mixed. The long vowel was often introduced again, as Ion. νηῦς ship.

[*] 41. Addition.—α, ε, ο are sometimes prefixed before λ, μ, ρ, ϝ (prothetic vowels). Thus, ἀ-λείφω anoint with oil, λίπος fat; ἐ-ρυθρός red (cp. Lat. ruber), ἐ-είκοσι from ἐ-（ϝ）είκοσι; ὀ-μόργνυ_μι wipe; ἐ-χθές and χθές yesterday, ἴ-κτις weasel (κτιδέη weasel-skin helmet) are doubtful cases.

[*] 42. Development.—A medial vowel is sometimes developed from λ or ν between two consonants; thus αλ, λα; αρ, ρα; αν (35 b). Also (rarely) in forms like Ion. βάραγχος = Att. βράγχος hoarseness.

[*] 43. Disappearance.—The ι and υ of diphthongs often disappear before a following vowel. Thus, ὑός from υἱός son, βο-ός genitive of βοῦ-ς ox, cow. ι and υ here became semivowels ([ιγλιδε], [υγλιδε]), which are not written. Cp. 148 D. 3.

[*] 43 D. So in Hdt. κέεται for κείεται lies, βαθέα for βαθεῖα deep.

[*] 44. a. The disappearance of ε before a vowel is often called hyphaeresis (ὑφαίρεσις omission). Thus Ionic νοσσός chick for νεοσσός, ὁρτή for ἑορτή festival; ἀδεῶς fearlessly for ἀδεέως. Here ε was sounded nearly like y and was not written.

[*] 44 a. D. Cp. Hom. θεοί A 18 (one syllable). ι becomes [ιγλιδε] in Hom. πόλιος (two syllables) Φ 567. ι rarely disappears: δῆμον for δήμιον belonging to the people M 213.

b. The disappearance of a short vowel between consonants is called syncope (συγκοπή cutting up). Thus πί_πτω fall for πι-πετ-ω, πατρός father for πατέρος. Syncopated forms show the weak grade of vowel gradation (35, 36).

[*] 45. Assimilation.—A vowel may be assimilated to the vowel standing in the following syllable: βιβλίον book from βυβλίον (βύβλος papyrus).

a. On assimilation in distracted verbs (ὁρόω see, etc.), see 643 ff., 652.