aardvark
bubble
accomodate
addition
freeze
off
goggles
withhold (are there any other double “h” words?)
skiing
hajj
bookkeeper
all
lemming
announce
moon
happy
qq? (equivalent to dividing by zero, I think)
terrible
glass
letter
vacuum (I think this is the only double uu in English?)
savvy
powwow
doxxing
sayyid
blizzard
Up to you if you want either of these to count as borrowed words.
I’ve rarely seen “seqq” and “et seqq” as an abbreviation for Latin “et sequentes”, meaning ‘in the following’. Usually it’s abbreviated “et seq” though. Compare “etc” and “et cetera”.
There’s a Middle Eastern spice blend that is translated with two (silent) 'q’s or 'k’s. My dictionary uses “dukka” or “dukkah”, but often times I see it in stores as “duqqa”.
An interesting side-discussion is how many double-letters from A-Z can we come up without using compound words?
So far, all the “hh”, “kk”, and “ww” words posted are clear compounds where both of the sub-words are in common use in their own right and with stand-alone meanings that map directly to their role in the compound word. All the other words I can quickly think of for those three letters are also compounds.
Yes, I admit the definition of a compound word is at least a bit subjective; compounds that entered the language enough centuries ago seem to us to be plain single words, while ones created just recently, e.g. chatbot, still seem like clearly two separate words glued together.
Which also points out a helpful feature of English: when adding “ing” to a word ending in a consonant, we often double that final consonant. If we wanted to rule those “-ing” endings as out of bounds we’d have yet a different permutation of the game.
With due respect, onomatopoeia is almost but not quite cheating. How exactly does one spell a Bronx cheer? I bet it’s one of the few English words with 5 (or is it 6?) consecutive Rs in it. Admittedly, your two examples are much more mainstream real words than mine.