sign, n. omen, auspice, portent, prodigy, prognostic, augury, foretoken, presage; mark, token, indication, symptom, index, emblem, symbol; trace, vestige, ensign, signal, beacon; gesture, motion; signature.  Associated Words:  ominous, portentous, augurial, semeiology, semeiological, sematology, semiotic, semeiography.

sign, v. signify, mark, indicate, betoken; subscribe.

signal, n. sign, ensign, beacon.  Associated Word:  pharology.

signal, a. memorable, remarkable, noticeable, notable.

signature, n. autograph, sign-manual.  Associated Word:  signatory.

signer, n. subscriber, signatory.

significance, n. meaning, import; consequence, importance, force.

significant, a. momentous, important; indicative, significative.  Antonyms:  insignificant, unimportant, meaningless.

signification, n. meaning, import, acceptation, sense.

signify, v. indicate, betoken, denote; mean; matter.

silence, n. stillness, quietness; taciturnity, muteness, reserve; secrecy.

silence, v. still, hush, quiet, suppress, lull, quell, appease.

silent, a. still, quiet, noiseless, inaudible; taciturn, reserved, mute; quiescent.

silkworms, n. pl.  Associated Words:  sericulture, mulberry, cocoon, filature, cocoonery, bombic, bombyx, filator, muscardine.

silky, a. sericeous, silken.

sill, n. threshold; window sill.

silliness, n. folly, foolishness, puerility, stupidity, inanity, inaneness, absurdity, senselessness, ineptitude.

silly, a. witless, foolish, simple, fatuous, imbecile, half-witted; stupid, unwise, inept, absurd, inane, nonsensical, senseless, puerile.

silver, n. argentum; bullion (uncoined silver).  Associated words:  filigree, platinum, desilverize, desilverization, patio, vermeil, fulguration, silversmith.

silvery, a. silver, argent, argentine, argentous, argentiferous.

similar, a. like, corresponding, resembling, homogeneous, analogous.

similarity, n. analogy, homogeneity, likeness, similitude, correspondence.

simile, n. comparison, metaphor.

simoon, n. desert wind, khamsin, samiel.

simper, n. smirk.

simple, a. incomplex, uncompounded, single, elementary, uncombined, mere; plain, unaffected, artless, naive, unsophisticated; credulous, gullible, silly, oafish.  Antonyms:  complex, complicated, intricate, artful, crafty, elaborate.

simpleton, n. dolt, dunce, numskull, lackbrain, oaf, witling, fool.

simulate, v. pretend, feign.

simulation, n. pretense, feint, feigning, affectation.

simultaneous, a. contemporaneous, synchronal, synchronous.

sin, n. iniquity, transgression, wickedness, delinquency, peccadillo, offense, peccancy, unrighteousness.  Associated Words:  ponerology, hamartiology, peccable, peccability, peccant, peccavi, impeccable, impeccability.