Matthew 17:21 But this kind goes not out except

Greek : 

This verse does not appear in the sources we used today. Below is the verse from the source used by the KJV translators.
Textus Receptus: τοῦτο δὲ τὸ γένος οὐκ ἐκπορεύεται εἰ μὴ ἐν προσευχῇ καὶ νηστείᾳ

Literal Verse: 

This on, however, this kind, doesn't go out except by prayer and fasting.

KJV : 

Matthew 17:21 Howbeit this kind goeth not out but by prayer and fasting.

Interesting and Hidden Aspects: 

This verse does not exist in the sources we use today.  The analysis is of the Textus Receptus version used by the KJV translators. The version in Mark 9:29 is shorter and uses a slightly different vocabulary.

Related Verses: 

Greek Vocabulary: 

Τοῦτο (pron sg neut nom) "That" is touto, which means "from here", "from there", "this [thing]," or "that [thing]."

δὲ (conj/adv) "Howbeit" is de which means "but" and "on the other hand." It is the particle that joins sentences in an adversarial way but can also be a weak connective ("and") and explanation of cause ("so") and a condition ("if").

τὸ (article sg neut nom) "The" is the Greek definite article, hos, ("the"), which usually precedes a noun and, without a noun, takes the meaning of "the one" or, in the plural, "the ones."

γένος [uncommon]( noun sg neut nom) "Kind" is from genos (genos), which means "race", "offspring", "class", "sort," and "kind."

οὐκ (partic) "Not" is ou which is the negative adverb for facts and statements, negating both single words and sentences. The other negative adverb, μή applies to will and thought; οὐ denies, μή rejects; οὐ is absolute, μή relative; οὐ objective, μή subjective.

ἐκπορεύεται "Goes out" from ekporeuômai, which means "to make to go out" and "fetch out."

εἰ μὴ (conj particle) "But" is ei me, which is the conjunction that means "if not", "but," and "except." εἰ is the particle use with the imperative usually to express conditions "if" or indirect questions, "whether." (me) is the negative used in prohibitions and expressions of doubt meaning "not" and "no."

ἐν (prep) "In" is en, which means "in", "on", "at", "by", "among", "within", "surrounded by", "in one's hands", "in one's power," and "with". -- The word translated as "in" also means "within", "with," or "among."

προσευχῇ ( noun sg fem dat ) "Prayer" is from proseuche, which means only "prayer." The verb form, proseuchomai, is usually used by Jesus in his teachings. This is the first time that the noun is used.

καὶ (conj/adv) "And" is kai, which is the conjunction joining phrases and clauses, "and," or "but." After words implying sameness, "as" (the same opinion as you). Used in series, joins positive with negative "Not only...but also." Also used to give emphasis, "even", "also," and "just."

νηστείᾳ ( noun sg fem dat ) "Fasting" is nesteia, which means "to fast."

KJV Analysis: 


Howbeit -- The Greek word translated as "howbeit" means "but", "however", and "on the other hand". Since it always falls in the second position, translating it as "however" often captures its feeling better. 

this -- The word translated as "this" means "from here" or "this/that thing."

untranslated -- The untranslated word is the Greek definite article. The Greek article is much closer to our demonstrative pronouns ("this", "that", "these", "those"). See this article for more. 

kind -- "Kind" is from an uncommon noun for Jesus that means "race", "offspring", "class", "sort," and "kind." The female form of the noun is the word translated as "generation."

goeth..out -- "Goes out" is from a verb which means "to make to go out" and "fetch out."

not -- The Greek word translated as "not" is the Greek negative used to deny objective facts, not opinions. It makes a negative statement of fact. Adding "really" to the sentence captures the same idea.

but -- This is not one of the two Gree words meaning "but." It is two Greek words arethat mean "if not" but this phrase is used to mean "except", "instead", and "but." 

by -- This comes from the following words that require the addition of a preposition in English to capture its meaning, a "to" as an indirect object, a "with" for instruments, an "in" for locations, an "as" for purposes, an "of" for possession, a "by" for agents, an "as" for comparisons, and an "in" for area of affect.

prayer -- -- "Prayer" is from the noun which means only "prayer." The verb from the same root is usually used by Jesus in his teachings. This is the first time that the noun is used.

and -- The Greek word translated as "and" is used as the conjunction "and", but it also is used to add emphasis ("also").

fasting. -- "Fasting" is from which means only "to fast." However, Christ usually used the noun form.