-сь

• IPA^(key): [sʲ]

-сь • (-sʹ)

1. contraction of -ся (-sja) (reflexive suffix appended to finite verbs and infinitives to make a reflexive, reciprocal, or intransitive verb)

• After a vowel, -ся is usually contracted to -сь, except when attached to an adverbial participle:
  • мы́ться (mýtʹsja, “to wash oneself”), мо́ется (mójetsja, “[she] washes herself”)
  • мо́юсь (mójusʹ, “[I] wash myself”)
  • мы́вшаяся (mývšajasja, “[who had] washed herself”).

Inherited from Proto-Slavic *sь (“this”). Doublet of сий (sij), a borrowing from Old Church Slavonic. See also сей (sej), the inherited independent form.

-сь • (-sʹ)

1. this, last (found in a few, mostly obsolete or dialectal, terms referring to time)

   ‎лони́ (loní, “year”) (dialectal) + ‎-сь (-sʹ) → ‎лони́сь (lonísʹ, “last year”) (dialectal)

   ‎вчера́ (včerá, “yesterday”) + ‎-сь (-sʹ) → ‎вчера́сь (včerásʹ, “yesterday”) (colloquial)

   ‎дне- (dne-, “day”) + ‎-сь (-sʹ) → ‎днесь (dnesʹ, “now”) (obsolete)

   ‎ле́то (léto, “year, summer”) + ‎-сь (-sʹ) → ‎ле́тось (létosʹ, “last year, last summer”) (low colloquial)