"Pithy"

I recently got a paper back from my "Morality and Religion" class. In the comments on that paper, my teacher informed me that I was basing the conclusion on three pithy arguments – a bad thing, apparently, in a philosophy paper.

Upon first reading this comment, I thought I understood his meaning: My paper was too informal, its arguments were not appropriately stringent, I was engaging more in demagoguery than in philosophy. However, after a moment, I realized that I was not entirely sure what "pithy" meant. I looked it up in my dictionary. Specifically, Webster's New World Dictionary of the American Language, Second College Edition.

(I have made a few minor edits to the entry, for purposes of typographical convenience. The definitions are unchanged, but the pronunciation guide and the other forms (adverbial, etc.) have been removed.)

pithy adj. 1. of, like, or full of pith 2. terse and full of substance or meaning—SYN. see CONCISE

This definition quite surprised me. I had thought that to be pithy was like being witty. My mental image, in fact, was of some Lord Peter Wimsey archetype (those ignorant of Dorothy Sayers' mystery novels may substitute Oscar Wilde or Jerome K. Jerome) making up silly proverbs. Such little phrases hardly seemed to fit this description. I resolved to search further, and thus I visited Merriam-Webster Online, which would presumably have a more recent definition than the 1980 college dictionary I had previously checked.

(Note that similar changes have been made to this definition. The full entry, however, can still be found through the link.)

Main Entry: pithy
Function: adjective
1 : consisting of or abounding in pith
2 : having substance and point : tersely cogent
synonym see CONCISE

"Curiouser and curiouser!" thought I, in a conscious imitation of Lewis Carroll. Clearly, this deserved further investigation.

I next proceeded to Wikipedia, thinking that it might contain more depth on the word. Unfortunately, no entry on "pithy" existed, and the entry on "pith" dealt purely with the vegetable sense of the term.

I continued to Google, testing the "definition" link on the results page. It forwarded me to answers.com.

Oddly enough, my answer was there. The first entry repeated the earlier ones ("[p]recisely meaningful; forceful and brief: a pithy comment."), the second was a thesaurus ("[p]recisely meaningful and tersely cogent: aphoristic, compact, epigrammatic, epigrammatical, marrowy. Informal brass-tacks. Idioms: down to brass tacks, to the point. See meaning, style/good style/bad style."), but the third, from "WordNet", had a slightly different answer:

The adjective pithy has one meaning:
Meaning #1: concise and full of meaning
Synonym: sententious

This led me naturally to the meaning of "sententious". According to the other page, this was:

1. Terse and energetic in expression; pithy.
   
2. 1. Abounding in aphorisms.
      
   2. Given to aphoristic utterances.
   
   
3. 1. Abounding in pompous moralizing.
      
   2. Given to pompous moralizing.
   
   

I stopped at this point, having found a definition matching my prior beliefs. A definition of the wrong word, perhaps, but still a definition.

Now that I think it over again, I wonder how good these definitions are. If I and those I know seem to use "pithy" more like "sententious" than like "concise", then are these dictionaries simply wrong, or am I? Is the conflict merely that of different English dialects? What is the answer?