slamang - a black gibbon of Sumatra that is the largest of the gibbons and has the second and third toes untited by a web.

sibilance, sibilatory, sibling, sieving, sigh (believe it or not, the heading of this page is “Words appearing Infrequently”

siglum - I couldn’t find a definition of this, though it was used in many places talking about management of data.
“An Authority has three attributes: a siglum which represents it in displays…”
could it be a corruption of Latin “sigillum = a seal, a signet”?

sigmoid - shaped like a letter “s”. In large bowel, segment before the “rectum” (which is straight)

signality, signet, signifier, signorina, Sikhism (relating to one of India’s religious groups) silencer,
silver (I kid you not = a word appearing infrequently!!!!!!!!!. similar (I can’t stand it) similitude

simoniac, simony - purchase of church office or preferment

simplicial, sincere, singlesticker (who cares what that is) singsong (a real dingdong put that one in)
sinistrad = towards the left, sinistration, sinkage,

Sinople: old French term for vert, and now always used by French heralds.


sinuate -

sn[u[ate 7sin4y1 it, 3at#; for v., 3at#8
adj.
5L sinuatus, pp. of sinuare, to bend < sinus, a bend6
1 SINUOUS
2 Bot. having an indented, wavy margin, as some leaves
vi.
3at#ed, 3at#ing to bend or wind in and out; be sinuous or wavy
sin$u[ate[ly
adv.
sin#u[a4tion
n.
siphonapterology - a branch of entomology dealing with fleas (it sucks)
siphorhinal - built like an elephant, no doubt
siriasis = sunstroke. That is inability to function because of circulatory disturbance resulting from excessive exposure to strong sunlight.
sirop = syrup, sisal = a fiber used in making rope. situation, sixsome, sizzling,

sellum
n.
5Early ModE < Du schelm, akin to OHG skelmo, one deserving to die < IE base *(s)kel3, to cut > SHELL, HELM26 [Chiefly Brit., etc.] a rascal; rogue; scamp: now common only in South Africa Also skelm 7skelm8
From Oz
“The word skerrick means “a small amount; a small fragment; the slightest bit”. It’s use is almost always negative: we might easily say that we don’t have a skerrick of something, but it would unusual to say that we do have a skerrick – unusual, but not entirely unknown,”

sketchy

skiagram = a type of X-ray

skiametry a use of skiagram to measure something

skiff - what you call a rowboat on Cape Cod and elsewhere

skiffle
n.
1 a former primitive style of jazz played by bands using some nonstandard or homemade instruments
2 a kind of up-tempo popular music like this, played as by jug bands, esp. in the United Kingdom in the 1950‘s, characterized by elements of jazz, blues, country, folk, etc.
skiing , skin (I want my money back! not that I paid any