Words are of two kinds, simple and double. By simple I mean those composed of non-significant elements, such as γ η. By double or compound, those composed either of a significant and non-significant element (though within the whole word no element is significant), or of elements that are both significant. A word may likewise be triple, quadruple, or multiple in form, like so many Massilian expressions, e.g. 'Hermo-caico-xanthus who prayed to Father Zeus.'
Every word is either current, or strange, or metaphorical, or ornamental, or newly-coined, or lengthened, or contracted, or altered.
By a current or proper word I mean one which is in general use among a people; by a strange word, one which is in use in another country. Plainly, therefore, the same word may be at once strange and current, but not in relation to the same people. The word σιγυνοΝ, 'lance,' is to the Cyprians a current term but to us a strange one.
Metaphor is the application of an alien name by transference either from genus to species, or from species to genus, or from species to species, or by analogy, that is, proportion. Thus from genus to species, as: 'There lies my ship'; for lying at anchor is a species of lying. From species to genus, as: 'Verily ten thousand noble deeds hath Odysseus wrought'; for ten thousand is a species of large number, and is here used for a large number generally. From species to species, as: 'With blade of bronze drew away the life,' and 'Cleft the water with the vessel of unyielding bronze.' Here αρυραι, 'to draw away,' is used for ταμειΝ, 'to cleave,' and ταμ ειΝ again for αρυαι, - each being a species of taking away. Analogy or proportion is when the second term is to the first as the fourth to the third. We may then use the fourth for the second, or the second for the fourth. Sometimes too we qualify the metaphor by adding the term to which the proper word is relative. Thus the cup is to Dionysus as the shield to Ares. The cup may, therefore, be called 'the shield of Dionysus,' and the shield 'the cup of Ares.' Or, again, as old age is to life, so is evening to day. Evening may therefore be called 'the old age of the day,' and old age, 'the evening of life,' or, in the phrase of Empedocles, 'life's setting sun.' For some of the terms of the proportion there is at times no word in existence; still the metaphor may be used. For instance, to scatter seed is called sowing: but the action of the sun in scattering his rays is nameless. Still this process bears to the sun the same relation as sowing to the seed. Hence the expression of the poet 'sowing the god-created light.' There is another way in which this kind of metaphor may be employed. We may apply an alien term, and then deny of that term one of its proper attributes; as if we were to call the shield, not 'the cup of Ares,' but 'the wineless cup.'
<An ornamental word …>
A newly-coined word is one which has never been even in local use, but is adopted by the poet himself. Some such words there appear to be: as ερνυγεσ, 'sprouters,' for κ ερατα, 'horns,' and αρητηρ, 'supplicator,' for ιερευσ, 'priest.'
A word is lengthened when its own vowel is exchanged for a longer one, or when a syllable is inserted. A word is contracted when some part of it is removed. Instances of lengthening are,—ποληο σ for πολεωσ, and Πηλ etaιαδεω for Πηλειδ ου: of contraction,—κρι, δω, and οψ, as in μια γινεται αμφοτερων οψ.
An altered word is one in which part of the ordinary form is left unchanged, and part is re-cast; as in δεξι—τε ρον κατα μαζοΝ, δεξιτεροΝ is for δε ξιοΝ.
[Nouns in themselves are either masculine, feminine, or neuter. Masculine are such as end in Ν, ρ, σ, or in some letter compounded with σ,—these being two, and ξ. Feminine, such as end in vowels that are always long, namely eta and ω, and—of vowels that admit of lengthening—those in α. Thus the number of letters in which nouns masculine and feminine end is the same; for ψ and ξ are equivalent to endings in σ. No noun ends in a mute or a vowel short by nature. Three only end in ι,—μηλι, κ ομμι, πεπερι: five end in υ. Neuter nouns end in these two latter vowels; also in Ν and σ.]
Poetics by Aristotle