-сь

Suffix

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

Usage notes

 * After a vowel, -ся is usually contracted to -сь, except when attached to an adverbial participle:
 * , мо́ется
 * мо́юсь
 * мы́вшаяся.

Etymology 2
., a borrowing from Old Church Slavonic. See also, the inherited independent form.

Suffix

 * 1) this, last

Etymology
, from.