The adjective is πλείους. With a little dictionary work, I see that it is the comparative form of πολύς, masculine nominative plural.
The masculine nominative singular seems to be πλείων.
The dictionary entry for πλείων gives me this: πλείων, πλέων, ονος, ὁ, ἡ. With this information, how do I find what I need to make a declension table for this adjective?
Surely every schoolboy knows how to do this, but I don’t. 
Hi I hope you will find this helpful from the Cambridge Grammar of Classical Greek:
Many thanks Seneca, for that information was most helpful.
Yes the tricky thing about these comparatives is that the -ους ending is not only acc.pl. (contracted from -ονας) but also **nom.**pl. (contracted from -ονες)!
Funnily enough, I have found that wiktionary (the wikipedia dictionary) is by FAR the best and easiest to use source for this kind of info (for Greek, Latin, or really any language that people might be interested in learning). It’s perfect for getting paradigms for nouns and verbs, and simple definitions, plus with links to dictionaries in the footnotes.
Generally, I just copy-paste any word that I don’t recognise into google, and if there is a wiktionary article for it (which there is about 95% of the time) its generally the first or one of the first results. So, with a 1-second google search, the first result was this page for πλείους, which then told me its a form of πλείων, and clicking on that then takes me to this page, with a definition and full paradigm of πλείων, plus links to a few different dictionaries.
It’s a super-duper useful resource that more people should know about.
I would just add a word of caution about wiktionary. Over the years people have posted things here from that source which are not correct. No doubt things have improved but one should always be wary of using “automatic” electronic resources. It is also much more useful I hope to use something like a published grammar because of the explanations provided. Its always best to understand why a declension takes a particular form.
Yes, that’s a fair caveat. It’s useful to easily find glosses and paradigms for most words, but more serious work will require a dictionary. Like I said though articles will generally have a link to the relevant articles in the references, which is handy.
I haven’t come across any errors in Wiktionary’s inflections, but it can get tricky to interpret their information when you have various Attic and epic alternatives.
Another good resource is the University of Chicago’s web site. It presents every form that has actually been attested, and no forms that haven’t. (I haven’t checked, but I assume they get their data from Project Perseus’s treebank.) Try going to logeion.uchicago.edu , then putting in πλείους. Click through to the link on Morpho. Again there can be problems when you’re trying to sort out what’s what dialect – unlike Wiktionary, they don’t even attempt to label the inflections by dialect.
For a precise picture using a specific dialect, I go to the Project Perseus treebank. So for example, if I look up πλείους in Homer, it tells me that it does exist in Homer, and it’s lemmatized as πλείων. Then further searching tells me what forms of the word occur in Homer. I’m sure there is some way to do this through a public web page, but I just have my own off-line script that I use, which is open source: https://github.com/bcrowell/ransom/blob/master/scripts/report_inflections.rb
$ ./scripts/report_inflections.rb πλείων gender=* number=* case=*
gender = m
singular
dual
plural
case = n
πλέονές (1), πλέονες (6), πλείους (1)
case = g
πλεόνων (1)
case = d
πλείοσί (1), πλεόνεσσι (2), πλεόνεσσιν (2)
case = a
πλέας (1), πλέονάς (1), πλέονας (4)
gender = f
singular
dual
plural
gender = n
singular
case = n
πλεῖον (1)
case = a
πλεῖον (1)
dual
plural
case = d
πλείοσιν (1), πλεόνεσσι (1)
case = a
πλείονα (5)
The given lemma πλείων is an exact and unique match to the database, including accentuation.
total matches: 15, total occurrences: 29
This tells us, for example, that the nominative plural in this dialect can be either πλέονες (more common, and is what I would have guessed), or πλείους (per mwh). I suppose what’s going on is that the contraction is optional, and Homer probably doesn’t do contractions as often as you’d see in Attic.
Many thanks for reporting that very interesting work, Ben. Have you seen the ios Attikos app?
Thanks for your kind words. No, I’m an open source guy, and I don’t own a cell phone. But I’m curious to hear about the app you refer to. What does it do, and do you like it?
Attikos provides a selection of classical Greek texts, and lets you, while reading one, touch on a word. When you touch the word, Attikos presents a parsing, and a short definition, both from Perseus, I believe. In this presentation, you can choose to see full defintions from several major dictionaries.
https://apps.apple.com/us/app/attikos/id522497233
I’m reading PLato’s Apology of Socrates. I study a paper copy. Sometimes I can sight-read a sentence, maybe one sentence in 10. I use Attikos on my ipad to look up unknown words, or when uncertain to get a parse. Usually after this I can make out the sentence, two sentences out of three, maybe. If I cannot make out a meaningful sentence, I check it against a translation, and try again. Each step of this produces topics for study and review. So I also have a couple of paper grammars handy.
I think for widely used texts a lexicon for each, on the model of New Testament lexicons, would be extremely helpful. A NT lexicon has an entry for every word-form in the NT. Usually there is a reference to a headword (aka lemma) with an extensive article.
This sounds very much like my current experience trying to plow through the Iliad. When I’m baffled, often I find that I just haven’t identified the subject of the sentence correctly. If it’s explicit, I can scan for whatever word is in the nominative case, but often the subject is implicit, and it doesn’t occur to me who it is. Homer also has a maddening tendency to have an adjective seperated by a considerable distance from the noun it’s modifying.
Socrates is a fascinating historical character. If I had a time machine, I would use it to go and find out about the real Socrates, rather than the character portrayed by Plato.