Long one-syllable words.
Here are some rarer examples, all of which are acceptable in international Scrabble: SCHLUMPED, SCHMEARED, SCHMEERED, SCHNORRED, SCRAICHED, SCRAIGHED, SCRAUGHED, SCRITCHED, SCROOCHED, SCROWDGED, SQUINCHED, SQUOOSHED, THRUTCHED
Before moving on to longer examples, let's disallow drawn-out monosyllabic noises and utterances such as the 234-letter cry of anguish (230 A's followed by 4 H's) on the last page of Portnoy's Complaint (1967) by Philip Roth.
BROUGHAMED (broomd) transported by brougham (a one-horse closed carriage), first used in 1854 in Household Words, an English weekly magazine edited by Charles Dickens.
"So on and on until the doctor of today grows upon us, learned, skilful, knighted, broughamed, degreed, honoured, ..." [Net]
SCHMALTZED imparted a sentimental atmosphere to. [OED]
SCHNAPPSED loaded up on the alcoholic drink schnapps.
"We will get very Schnappsed--very, very Schnappsed! We will talk about the good things!" [The Book of Kings, J Thakara, 2000, p469]
SCHPRITZED attacked, slandered. [CDS]
SCHWARTZED responded 'Schwartz' to a player without making eye contact, in the drinking game Zoom Schwartz Profigliano. [Wiki]
SCRAUNCHED a dialectic word for 'crunched'. [Web3]
SCREECGHED Shetland Islands variant of 'screighed', shrieked. [EDD]
SCREETCHED variant of 'screeched'. [EDD]
SCRIETCHED early form of 'screeched'. [OED]
SCROANCHED a Cornish word meaning 'scraped'. [EDD]
SCROONCHED variant of 'scrunched', squeezed together. [Web3]
SCROOTCHED variant of 'scrooched', crouched. [RHD]
SCROUNCHED variant of 'scrunched', crunched. [EDD]
SKLEUTCHED slouched, a Scottish term. [EDD]
SKRIETCHED early form of 'screeched'. [OED]
SPLAUTCHED let a soft substance fall heavily on the floor. [EDD]
SPRAUNCHED exaggerated, told lies. [EDD]
SQUAITCHED squeezed out of shape. [EDD] The associated 17-letter SQUAITCHED-MOUTHED (lying, deceitful) is the longest known 2-syllable dictionary term.
SQUAWTCHED variant of 'squatched', betrayed, told a secret. [EDD]
SQUIRRELED variant of 'squirrelled' (see 11 Letters).
STHRITCHED strutted, put on airs. [EDD, stretch]
STRAUNCHED old variant of 'stranged', obsolete for 'estranged'. [OED]
STRENGTHED obsolete for 'strengthened'. [OED]
STREYGHTES old form of 'straights', narrow passes. [MED, streit]
STROOTCHED variant of 'strooched', dragged the feet while walking. [EDD]
There are no doubt other 10-letter monosyllables that can be added to this list. Now it is time to look at the small, curious collection of longer one-syllable terms, which comprises dialectic and obsolete words, English and part-foreign coinages, and examples of strained verbal inflections and regional pronunciation.
BROUGHAMMED (broomd) somewhat dubious double-m variant of broughamed (see 10 Letters), suggested by American poet William Harmon in a competition to find the longest monosyllabic word. [Wiki]
SCHWEPPESED a few years back American actress Uma Thurman starred in a raunchy global TV/cinema campaign for Schweppes soft drinks. The following comment was posted on brandchannel.com [Net] on 6 May 2011:
"[Thurman] is a little more offbeat than her typical characters and certainly more sexed up (or at least Schweppesed up), than normally depicted on screen."
SPLEAATCHED variant of 'splatched', splattered. [EDD]
SQUIRRELLED (squerld) stored up for future used. A compressed American pronunciation sanctioned by the Merriam-Webster Online Dictionary. [Wiki, Net]
STRENGHTHED variant of 'strengthed'. [MED, strengthen]
STREYNGTHES early form of 'strengths'. [OED]
SCHTROUMPFED (shtroompft) the original French name for 'smurf' (you know, the cute little blue characters) is schtroumpf, which is used as an all-purpose noun and verb by Smurfs and in imitation of them. The form schtroumpfed is used in an English translation of an essay by Italian writer Umberto Eco:
"Let us suppose an English speaker of average culture hears a Schtroumpf poet reciting 'schtroumpfed lonely as a schtroumpf.'"
However, this is intended to represent the Schtroumpf language rather than English. [Wiki]
STRENGTHEDST a possible archaic second person singular past tense of the obsolete verb 'strength', to strengthen. For example, the Bible contains the following:
'In the day when I cried thou answeredst me, and strengthenedst me with strength in my soul.' (Psalms 138:3)
The 12-letter form strengthedst would be feasible, and indeed does appear (in error) on some websites and in a published book. [Net]
While the-edst ending would usually be pronounced as a separate syllable from the verb stem, it could conceivably be shortened to a single syllable.
STREYNGHTHED another variant of the old word 'strengthed', strengthened. The verbal stem streynghth- is listed in MED, and the following appears in a medieval manuscript held at Durham University Library, England:
"Alexander the grett conqueroure in all his conquest ... and stallwardly streynghthed hyme in all vertu." [www.dur.ac.uk (Net)]
SCHTROUMPFFED a nonce-word based on Schtroumpff, variant of 'schtroumpf', French for 'smurf' (see 12 Letters). The double-f ending is used numerous times as a nickname by people registered on the social networking website Facebook (Net). For example, there is a Schtroumpff Blue, Schtroumpff Amoureux, Schtroumpff Grognon, and Schtroumpff Gourmand, as well as a Cynique Schtroumpff, Grand Schtroumpff, Marie Lola Schtroumpff Allizon, and others. One could easily say after being swamped by all those Schtroumpffs, "We're just about Schtroumpffed out!"
STRENGHTHEDST possible Middle English variant of 'strengthedst' (see 12 Letters), based on the form 'strenghthed' (see 11 Letters), as in 'thou strenghthedst'.
HALFPENNYWORTH (haypth) as much as is sold for or is worth a halfpenny (hape-nee), a compressed British regional pronunciation. The word is often pronounced and spelt 'ha'porth or 'ha'p'rth (hay-pith.) However, in a land where the surname Cholmondeley can be shortened to 'Chumley' and Featherstonehaugh to 'fenshaw', compression to a single syllable is possible, as suggested by the occasional spelling 'ha'p'th'. [Net]
"With the disappearance in the 1980s of the halfpenny ..., the English are now denied the rich satisfaction of compressing 'halfpennyworth'
into 'haypth'." [The Mother Tongue, Bill Bryson, 1990]
STREYNGHTHEDST possible Middle English variant of 'strengthedst' (see 12 Letters', based on the form 'streynghthed' (see 12 Letters'), as in 'thou streynghthedst'.
HALFPENNYWORTHS (haypths) plural of 'halfpenny worth' (see 14 Letters).
CDS Cassell Dictionary of Slang, Jonathon Green, 1998
EDD English Dialect Dictionary, Joseph Wright, 1970 ed.
MED Middle English Dictionary, 1959-2001
Net Internet, using Google search program
OED Oxford English Dictionary, 2nd ed., 1989
RHD Random House Dictionary of the English Language, 2nd ed., 1987
Web3 Webster's Third New International Dictionary, 1976
Wiki Wikipedia (Net)
Hastings, New Zealand