Guard yourselves from the yeast that is an outward show of the separated.
Again, we see an attempt to make the Greek of Luke seem more like the Greek of Matthew and Mark
"Beware" is from a Greek verb which means "to hold to", "to offer", "to turn toward a thing," and "to pay attention." Only in the NT is it ever translated as "beware." The idea is not to be distracted.
The word translated as "of" is not the normal "of" that indicates possession. It is a very different word that means "from" in both location and when referring to a source. Here, it is referring to the "leaven" as the source.
"Leaven" means "yeast" the culture that spreads through flour to create the "bubbles" that make bread rise. It is Christ's symbol for ideas that propagate themselves. Christ compares the kingdom of heaven to leaven as well and the ideas of the Pharisees.
The Pharisees is a Greek word that means "dedicated" or "separated". They saw themselves "separated from common people as those more dedicated to following all the purity rules of tradition.
The word translated as "hypocrisy" is the Greek source of the English word. Our sense of its meaning comes from Christ's use of it. It is from the same root as the word for "actor," hypocrites, which also isn't translated. This word means, among other things, "to play a part."
Προσέχετε(verb 2nd pl pres imperat act) "Beware" is the Greek prosecho, which means "hold to", "to offer", "turn to or toward, ""to turn your mind toward, ""to be on one's guard against", "to take heed", "to pay attention", "to devote oneself to", "to attach oneself", "to continue", "to hold fast to [a thing], ""to have in addition," or "pay court to."
τῆς ζύμης (noun sg fem gen) "Leaven" is sometimes translated as "yeast." It is from the Greek zyme, which means any kind of bread or beer "yeast." It is from a root word meaning "to mix." This was a time when yeast didn't come in little packets but was maintained as a live culture, in this case, in the raw bread dough itself.
ἐστὶν (verb 3rd sg pres ind act) "Is" is eimi, which means "to be", "to exist", "to be the case," and "is possible." (The future form is esomai. The 3rd person present indicative is "esti.") -- When the verb "to be" appears early in the sentence before the subject, the sense is more like "it is" or, in the plural, "there are." -- The verb "is" here is the common form of "to be" in Greek. It means to have a certain characteristic or remain in a certain condition.
τῶν Φαρισαίων. (noun pl masc gen) "Pharisees" is from Pharisaios, which means "the separated", "the separate ones", " separatist" and refers to the religious sect. The word comes from the Hebrew, pharash, which means "to distinguish." this is the primary meaning of the Greek word krino, which is usually translated as "judge" in the Gospels. What we describe as "pure" or "sacred" was described in Hebrew as "separate," that is, separate from everyday items.