One of my friends argues that princessship is the only word which has 3 identical letter comes together (s) ,but I think there is no word such as princessship.
Can anyone tell me whether this is a real word, and if there are any more English words which have 3 letters consecutively?
There is no word with three consecutive letters under the most narrow definition of "real word", but there are several words of the following types:
There are many acronyms/initialisms that contain triple letters, like AAA, AIEEE, KKK, WWW, or Roman numerals like xviii.
There are place names, like
There are names of people with all sorts of unconventional spellings, like Minnnie, Annnora, or Diannne.
There are interjections like mmm, hmmm, zzz, etc.
There are archaic/poetic words with elided letters, like whenceeer (really, whencee'er from whenceever), wheree'er, etc.
Finally, there are words which would probably be written with a hyphen whenever used, like frillless (mentioned by Dusty) which is really frill-less, similarly bulllike, gulllike, wallless, many words ending in -ss-ship like your princessship, bossship, goddessship, headmistressship, patronessship.
I'm not a native speaker, but I'm under the impression that words with the same letter repeated three times are either elided so that they contain two, or are spelled with a hyphen.
For instance cross-section (hyphenated) or chaffinch (where the 3rd 'f' is omitted)
I believe princessship is typically spelled with a hyphen princess-ship, although I do remember references to it without. However, if your friend is willing to allow princessship as a word, certainly words like dutchessship, governessship, countessship, etc. would also qualify.
So one way or another, you can prove your friend wrong =D
Edit: A quick search also brings up frillless which has an entry in OED
Discounting acronyms, for words without hyphens that have three consecutive letters, the OED lists these:
brrr, countessship, duchessship, frillless, governessship, grrr, grrrl, hostessship, postmistressship
For words that have a letter, a hyphen, then that same letter twice repeated, it lists these:
eve-eel, paste-eel, salpingo-oöphorectomy, salpingo-oöphoritis, slime-eel, snipe-eel, spine-eel
For words where you have the same letter twice, then the hyphen, then that same letter again, it has all these:
ass-ship, ball-less, ball-lightning, ball-like, bee-eater, bell-less, boss-ship, boss-shot, boss-stone, brass-smith, burgess-ship, call-letter, call-loan, carcass-shell, cell-layer, cell-less, cell-like, cell-lineage, cell-lined, chaff-flower, class-subject, compass-saw, compass-signal, compass-stock, cross-saddle, cross-sea, cross-section, cross-sectional, cross-sectioning, cross-seizing, cross-sell, cross-shed, cross-shoot, cross-shot, cross-sleeper, cross-spall, cross-spider, cross-springer, cross-staff, cross-stitch, cross-stone, cross-street, cuckoo-orchis, cypress-spurge, demigoddess-ship, distress-sale, doll-land, dress-shield, egg-glass, fall-leaf, fall-less, fee-estate, fee-expectant, frill-lizard, fusee-engine, gall-leaf, gall-less, gill-lamella, gill-less, gill-lid, glass-sand, glass-shaped, glass-shell, glass-shrimp, glass-slag, glass-snail, glass-snake, glass-soap, glass-sponge, goddess-ship, grass-seeder, grass-siding, grass-snake, grass-snipe, grass-sparrow, grass-spirit, grass-sponge, grass-spring, head-mistress-ship, ill-less, ill-lived, ill-looking, ill-lookingness, isinglass-stone, Jaycee-ette, joss-stick, kill-lamb, kiss-sky, knee-elbow position, mastiff-fox, mill-lands, mill-leat, mill-lodge, miss-stays, mistress-ship, moss-seat, moss-starch, no-see-em, off-faller, off-falling, off-farm, off-field, pass-shooting, patroness-ship, poss-stick, press-shy, press-stone, press-stud, princess-ship, process-server, puff-fish, quill-less, seamstress-ship, see-er, see-everything, shell-less, shell-lettuce, shell-lime, skull-less, small-leaved, smell-less, stall-literature, still-liquor, stress-strain, three-edged, three-eight, till-land, toll-lodge, troll-line, wall-less, wall-lining, wall-lizard, well-laboured, well-labouring, well-laced, well-laden, well-laid, well-languaged, well-learned, well-leaved, well-led, well-legged, well-lettered, well-lighted, well-liked, well-liking, well-limbed, well-limned, well-lined, well-lit, well-liveried, well-living, well-loaded, well-lodged, well-looked, well-looking, well-loved, well-lunged, will-less, will-lessly, witness-stand, zoo-organic
Alas, there appear to be no instances of four letters in a row, even if separated by a hyphen or an apostrophe, such as *Kwanzaa-aardvark, *frisbee-eel, *tatoo-ooze, *install-llama, or *chimpanzee-eerie.
I see a product opportunity here. :)
How about "Wiiitis"? Although I'm not sure the word is considered a "real word".
Wiiitis -- pronounced “wee-eye-tis” -- is the latest ailment to develop from the video game era https://www.reuters.com/article/us-wii-elbow/if-its-not-tennis-elbow-it-may-be-wiiitis-idUSN0616721120070606
