Is cruel standard use as a noun in poetry? Are there terms for non-standard English specifically in regard to use in poetry?

Question

I hope this question isn't off-topic.
I heard a madrigal with the following verse which bothers me somewhat, grammatically.

Cruel, wilt thou persever?
Peace to leave ever?
Peace shalt thou have and gladness,
But when in sadness,
When thou the morn seest ev'n,
To fall from heav'n.

Thomas Morley (1597)
http://www1.cpdl.org/wiki/index.php/Cruel,_wilt_thou_persever_

Cruel seems to be used as a noun instead of an adjective. Is this non-standard or common use of the time? Even if so, and allowing for poetic license, how is this to be understood: personifying cruelty and addressing it or some other way? Also, but are there separate terms for the following kinds of liberty taken in poetry?

1. terms for using non-standard grammar from an unexpected part of speech (as in cruel wilt thou persever?) or a double negative, (as in I can't get no satisfaction - Rolling Stones) in a line in order to get the lines to scan?
2. a term for using a contractions to get the lines to scan, as in ev'n and heav'n
3. I was able to find a term for using a word to rhyme that doesn't quite rhyme, as in come, one and home or ev'n and heav'n: (assonance), but feel free to correct me if I'm wrong.

Answer 1

My guess would be that cruel is used to indicate a person or something personified: oh, cruel one—not cruelty.

1.) If a poet uses uncommon instruments confined to poetry in order to fit the metre/rhythm of his verse, he is said to be using them metri causa, "for the sake of metre" (Latin). I don't think there is any more specific term to match your examples.

Using a double negative to mean a (strong) negative is now just slang, which can be used as a figure of speech.

Using a double negative to mean a (strong) positive is called litotes:

There was no lack of willing maidens.

2.) Omitting letters (mostly vowels) in the middle of a word is called syncope.

3.) [Edited:] Assonance means simply that you use two words or syllables in close proximity that (only) share the same vowel sound, as opposed to consonance, where they share the same consonant sound. If they share initial consonants, it is called alliteration.

Assonance: of lock and pot

Consonance: all the levels will collapse

Alliteration: seven sodden sisters

Your example ev'n–heav'n would be consonance; there might be a word for semi-assonance, but I don't know any. I'm not sure what to make of come–one–home: it is conceivable that their vowels were identical in 16th-century pronunciation. Even and heaven might even have rhymed in the 16th century—I don't know.

Answer 2

No, it is not common to use "cruel" as a noun; but I think it is actually being used more or less as a name.

Answer 3

This is very poetic usage, where anything doesn't always 'go' but there sure is a lot of leeway. The poet probably didn't think the noun form 'cruelty' word fit the meter.

So it would be ungrammatical in most any variety of everyday spoken English to use 'cruel' as a noun, even personified.

Poets take liberties with all sorts of things, pronunciation, syntax, word meaning, etc., in order to fit some arbitrary meter or rhyme scheme

Answer 4

Cruel, wilt thou persever?

The "cruel" used here is referring to Cruelty in general. Poetry sometimes addresses a character value as a person, i.e.

The first was a fair maid, and Love her name;
The second was Ambition, pale of cheek,
or

And Joy, whose hand is ever at his lips

This was just a practice in older poetry. Morley, in your example, was addressing the character value of Cruelty.

N.B. The quotes were taken from John Keats.