A guess the word game
Ruby, 418 bytes, score 12 (on 'palest')



$dict = File.readlines('agreeddict.txt').map(&amp;:chomp)

def search(wrd)
  words = 0
  fdic = $dict.clone
  guess = ''
  starters = ['earths','blowup','coding']

  chs = wrd.chars

  while guess!=wrd do
    guess = starters.pop || fdic.pop
    words += 1
    ghs = guess.chars
    chars = (chs|ghs).size
    fdic.select!{|w|(w.chars|ghs).size == chars}
  end

  words
end

upp = 0;

p $dict.map{|w|
  [search(w),w]
}.max


Try it online!

Runs in 15 seconds on my machine.

TIO link for reference only - does not work if the file is not in the current directory.

The trick

Instead of brute-force elimination, try a list of initializers first. A lot of words differ by only 1 character and it's easy to get stuck in a single-letter elimination loop.

The most difficult words to guess are those with 4-5 very common characters (a e r s t), 1-2 'outsiders' (c p x z...) and some anagrams in the dictionary.

For example, when we reach a word containing the letters "a e r s t" and the answer is 5: if we just filter all the entries containing these 5 characters, we are left with a dictionary of 40 similar words, and then we have to try almost all of them, removing only a few words at each step.

We need to remove these words first, and we filter on the least common character, so if we get to "earths", and Player 1 answers 5, we don't have a lot of words to check. The first 2 words we always check are "coding" and "blowup" (no pun intended).

Now we can try with  a word containing the 5 most common letters ("earths"). If the answer is 4 or 5 (which is likely), we don't have a lot of words to choose from, because we already filtered all the words containing only 1 or 2 uncommon letters (and we only used 3 guesses to get here).

Finding the right initializers was a little tricky, I started with a list of 5 "quasi orthogonal" words (with as few letters as possible in common, a good start was "sporty fuzing hawked climax jumble", missing only the letter z) and got to 13, then started a test on automatically generated smaller lists.

'palest' seems to be a worst case, having 6 anagrams and 4 very common letters, but it's not the only word requiring 12 guesses, so I don't think I could get a better score with this approach.

I don't want to golf this.