This verse has a lot of surprises, especially considering that version of this saying are also offered in Matthew and Mark.  The biggest change is in a rephrasing to create a different "punchline" at the end. The other verses begin with the idea of tripping up little ones, this one ends with it in a way that is clearly meant to make a point. This seems like an evolution of the verse, very much in keeping with Jesus's humorous style. 

The "it would better" is said in three different ways in the three Gospels, but this is hidden in translation. Here a unique word is used, one that means to "indemnify for expenses incurred ", "pay for expenses incurred ", "pay what is due", "profit", and "gain an advantage".

The word translated as "for him" is the Greek word commonly translated as third-person pronouns in English.  The word means "the same" when used as an adjective. In the adverbial form, it  means "just here" or "exactly there." 

The "that" here is really an "if", the expresses a condition but it means nothing regarding whether that condition is met or not. It also means "if ever" and "whenever."

"Mill" is from a word that means "for a mill." It follows the word for stone.

The Greek word translated as "stone" means "a stone", "stone as a substance," and various specific types of stones, such as touchstones and altar stones.

"Were hung" is from a verb that mean "to hang" and, in the passive, "to be hanged." Interestingly, it also has a little of the sense we used in phrases such as to be "hung up" on something as in to be "wholly taken up with it." The odd thing is that this is in the present tense not a past tense so "hangs itself".

The Greek word translated as "about" means It means "around" when referring to a place, but, in this context, it means "about", "concerning", "on account of," and "in regard to." This is the way Christ usually uses it.

The word translated as "his" is the Greek word commonly translated as third-person pronouns in English.  It appears after "neck". The form is "that thoat of his". 

"Neck" is from the Greek word that means "neck" and "throat."

The Greek word translated as "and" is used as the conjunction "and", but it also is used to add emphasis ("also"). In a series, it is best translated as "not only...but also." After words implying sameness "as".

"He cast" is another unique verb for Jesus to use that means to " throw", "cast", ahd " hurl". This word is strange for many reasons. First, one of Jesus's favorite words means "cast" but in a more humorous sense. That word is used in the Mark version. Second, the tense is something completed in the past when the hanging of the stone is in the present.  We also saw this difference in tenses in Mark, even those a different "cast" was used. In Matthew, which uses a word meaning "drowned" here, the tenses of both words is past. Finally, as in Mark, this word is not passive, but the form where the subject acts on himself. "He has hurled himself".

The word translated as "into" means "into" a place, "towards" as a direction, "in regards to" a subject, and "up to" limits in time and measure.

"The sea" is from a word that means also means "sea" or "sea water."

"Than" is translated from a Greek word that means primarily "or" but serves as "than" in a comparison.

The word translated as "that" is an adverb or a conjunction that starts a subordinate clause "there", "where," and "in order that." This is a very different word that the "that" near the beginning of the verses.

The key word here is translated as "he should offend." It is a "Greek" form from an Aramaic verb that is found only in the Bible. It refers to putting a stumbling block before someone so that they trip and thereby offending them. In English, we would simply say, "trips you up." Though it doesn't sound like it in English translation, Christ uses this word to make light of his affect on the thinking of others.

The "one" here appears at the end of the verse, flipping the order in the other version. This makes it the punchline, emphasizing the idea of just "one".  Greek word translated as "one" means "one" (as opposed to other numbers), "single," and "one and the same."As in English, it can be used as a pronoun, meaning a single person.

"Of these" is a demonstrative pronoun that means "this", "here", "the nearer," and "the familiar." It appears after the "little ones".

"Little ones" is from an adjective, used as a noun, which means "small", "little," and "young." So, "the little" or, in the plural as used here, "little ones." See this article about the words Jesus uses for children.