This observation was obviously humorous. Again, the joke is apparent in Greek because the phrase has the classical joke form, setup and punchline, so the meaning isn't clear until the final word. The  first part of the setup is "truly, I'm telling you", which is a catchphrase that tells us a joke is coming. Then comes the specific part about the widow, which is drawn out, and seems to be saying that the woman is poorer that all, but the final word, "tosses", a word Jesus often uses comically, changes the meaning in the punchline, saying that she has tossed away more than all. The use of this word is also funny because it has the sense that this money was wasted, giving it to the temple.

 "Of a truth" is a Greek adverb no commonly used by Jesus in the other Synoptic Gospels. It is used frequently by all the Gospel writers, but it only appears in Luke three times to replace the Aramaic word ("amen") that Jesus uses in the other versions of these verses. John does have Jesus using it, but only in the sense of "indeed". 

The word translated as "I say" is the most common word that means "to say," and "to speak," but it also means "to teach," which seems to be the way Christ uses it more frequently. It also has many ancillary meanings such as "to count" ("to number" or like we might say, "to recount" a story) or "to choose for yourself." Christ usually uses this word to refer to his own speaking or teaching.

The Greek pronoun "unto you" here is plural and in the form of an indirect object, "to you", "for you", etc. 

The word translated as "that" introduces a statement of fact or cause.

"This" is translated from a Greek word that means "this", "that", "the nearer." It appears after widow, drawing out the statement.

"Poor" is an adjective that means "a beggar" and "beggarly" and it a metaphor for being lacking in something. It have an article "the" before it, making it a noun, "the beggar" or "this beggar" because the "this" is before it. The purpose here is to focus on the woman's poverty, making it seem as though that is what the comparison is about.

"Widow" is an adjective that means "widowed" or more generally, "bereaved".  Christ uses it as a noun because it has an article before it. 

The word translated as "hath cast in" has a number of meanings revolving around "throw" as we do in English with both "throw" and "toss." Jesus often uses this word humorously in the same way we use "dump" in English. This word comes at the end. It is the punchline because the rest of the verse makes it unexpected. The sense is more "tossed away" the "cast in".

The Greek word translated as "more" is an adjective that means "more" in many different senses of the word. However, its form doesn't seem to match any of the nouns in this part of the verse. The word follows the word for "beggarly" making it look like that is what is being compared.

The word translated as "than they all" is the Greek adjective meaning "all", "the whole", "every," and similar ideas. When it is used as a noun, we would say "everything" or "everyone".  It is in a form that makes it what is being compared so the "than" comes from it form, the the "more" before.