Luke 19:42 If thou hadst known, even thou, at least in this thy day, the things which belong unto thy peace! but now they are hid from thine eyes.
If you knew in this day in this way, even you yourself, the ones on the side of peace! Now, however, it has been buried from those eyes of yours.
The KJV adds a lot of "thy's" that do not exist in the Greek. It also changed the number of the final verb.
The "if" here expresses a condition but it means nothing regarding whether that condition is met or not. It also means "if ever" and "whenever."
"Thou hadst known," is a verb that means "to know", "to recognize", "make known", "to know carnally," and "to learn.
The Greek word translated as "even " is used as the conjunction "and", but it also is used to add emphasis ("also") and "even", as hear.
The "thou" here is the pronoun. Since pronouns are not usually used for subject in Greek, its use is to accentuate the word like we would say "you yourself".
There are no Greek words for "at least" in the Greek source we use today.
The word translated as "in" also means "within", "with," or "among."
The "this" is a pronoun that can mean "this" or "that," the nearer or the further depending on usage. As an adverb it can mean "therefore" and "that is why." It is not typically used as an adjective. The adverb, "in this way", seems more likely.
There is no "thy" in the Greek we used today. It originated in Latin Vulgate.
The Greek word translated as "day" also means "time," in general, and refers specifically to the "daytime." The article before the noun can be read as "this" without the pronoun.
The word translated as "the things " is the Greek definite article, which usually precedes a noun and, without a noun, takes the meaning of "the one." The "things" comes from the form, plural neutral. The Greek article is much closer to our demonstrative pronouns ("this", "that", "these", "those"). See this article for more.
There is no "which belong" either in the Greek we used today or in the Greek the KJV translators used.
The word translated as "unto" means "towards", "by reason of (for)," and "against."
There is no "thy" in the Greek we used today. It originated in Latin Vulgate.
"Peace" is the Greek term that means harmony between individuals and nations" and the general idea of safety, security, and prosperity. It is the opposite of the state of war. In Hebrew, the word for peace was used in salutations and as an inquiry as to one's health.
The Greek word translated as "but" 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.
The Greek word translated as "now" means "now", "at the present moment","presently," and "as it is."
The word translated as "they are hid" means to "dig up", "dig through", "dig into", but also means to "bury" but it has a number of other specific uses as well. The form is singular, passive, not plural. It doesn't refer to the "things" but to the "peace".
The word translated as "from" means "from" in both location and when referring to a source.
The word translated as "thy" is the possessive form of the second person pronoun.
The Greek word for "eyes" is the more technical terms for "eye" but it also means "sight". It is a metaphor for "cheer."
Εἰ (conj) "If" is ei, which is the particle used to express conditions "if" (implying nothing about its fulfillment) or indirect questions, "whether." It also means "if ever", "in case," and "whenever." It is combined with various conjunctions to create derivative conditions.
ἔγνως (verb 2nd sg aor ind act) "Thou hast known," is ginosko which means "to learn to know", "to know by reflection or observation," and "to perceive."
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".
τῇ ἡμέρᾳ (noun sg fem dat) "Day" is hemera, which, as a noun, means "day" "a state or time of life", "a time (poetic)", "day break" and "day time." It is also and also has a second meaning, of "quiet", "tame (animals)", "cultivated (crops)," and "civilized (people)."
ταύτῃ (adv/adj sg fem dat) "These things" is tauta, which is a referring pronoun meaning "these", "this", "that," and "here." It can mean the nearer or the further depending on usage. As an adverb it can mean "therefore" and "that is why."
καὶ (conj/adv) "Even" 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." --
σὺ (pron 2nd sg nom) "Thou" is su which means "you" and "your." --
τὰ (article pl neut acc) "The things" is the Greek definite article, which usually precedes a noun and, without a noun, takes the meaning of "the one" or, in the plural, "the ones."
πρὸς (prep) "Unto" is pros, which means "on the side of", "in the direction of", "from (place)", "towards" "before", "in the presence of", "in the eyes of", "in the name of", "by reason of", "before (supplication)", "proceeding from (for effects)", "dependent on", "derivable from", "agreeable,", "becoming", "like", "at the point of", "in addition to", "against," and "before." --
εἰρήνην (verb pres inf act or noun sg fem acc ) "Peace" is eirene, which means "time of peace," "national tranquility," "peace", "tranquility,""personal tranquility," and "harmony." It is the name for the goddess of peace.
— νῦν (adv) "Now" is nyn (nun), which means "now", "at the present moment", "at the present time", "just now", "presently," and "as it is."
δὲ (conj/adv) "But" 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").
ἐκρύβη [uncommon] (verb 3rd sg aor ind pass) "They are hid" is from krypto, which means "to hide", "to cover", "to bury", "to conceal", "to keep secret," and "to lie hidden." --
ἀπὸ (prep) "From" is apo, a preposition of separation which means "from" or "away from" from when referring to place or motion, "from" or "after" when referring to time, "from" as an origin or cause.
ὀφθαλμῶν (noun pl masc gen) "Eyes" is ophthalmos, which means "eye", "sight", "the dearest and best", "light", "cheer", "comfort," and "the bud [of a plant]."
σου.(adj sg masc gen) "Thy" is sou which means "of you" and "your."