letter-boxed.py

import collections
import urllib
import sys

sides = [arg.upper() for arg in sys.argv[1:]]
letters = set("".join(sides))

word_list = urllib.urlopen("https://raw.githubusercontent.com/dwyl/english-words/master/words_alpha.txt")
# word_list = open("/usr/share/dict/words")

def is_letterbox_word(word, index={l: i for (i, side) in enumerate(sides) for l in side}):
  if len(word) < 4:
    return False

  if not all(letter in letters for letter in word):
    return False

  last = -1
  for letter in word:
    if index[letter] == last:
      return False
    last = index[letter]
  return True

index = collections.defaultdict(lambda: [])
for line in word_list:
  word = line.strip().upper()
  if not is_letterbox_word(word):
    continue

  index[word[0]].append(word)

for word1 in sorted(word for words in index.values() for word in words):
  for word2 in sorted(index[word1[-1]]):
    if letters == set(word1+word2):
      print("%s > %s" % (word1, word2))

letter-boxed.sh

function perms() {
  a=$1
  b=$2
  c=$3
  echo "$a$a|$a$b|$a$c|$b$a|$b$b|$b$c|$c$a|$c$b|$c$c"
}

cat /usr/share/dict/words | 
tr "[A-Z]" "[a-z]" | 
grep -E "^[ramtuynohlip]+$" | 
grep -v -E "$(perms r a m)" |
grep -v -E "$(perms t u y)" |
grep -v -E "$(perms h o n)" |
grep -v -E "$(perms l i p)" |
awk '(length($1) >= 3) { print length($1), $1 }' |
sort -rn |
awk '{print $2 }'