со-

со- • (so-)

1. A prefix indicating unity or connection, akin to co-.

   ученик

   соученик

   student

   classmate

   работа

   соработка

   work

   cooperation, collaboration

2. A prefix indicating composition, akin to syn-.

   стави

   состави

   put

   put together, assemble

• IPA^(key): [sə]
• IPA^(key): [ˈso] (when stressed)

From Proto-Slavic *sъ(n)- (see с- (s-) and Proto-Slavic *sъ(n) for more information). The yer sound -ъ- was treated as strong when another yer followed in the next syllable, and was vocalized to -o-, whereas the yer in the next syllable was deleted, producing a consonant cluster.

со- • (so-)

1. Alternative form of с- (s-) (used before certain consonant clusters)

Borrowed from Old Church Slavonic съ- (sŭ-), from Proto-Slavic *sъ(n)-; see above.

со- • (so-)

1. with, con-, co-

   ‎со- (so-) + ‎гласи́ть (glasítʹ, “to say”) + ‎-ся (-sja) → ‎согласи́ться (soglasítʹsja, “to consent”)

   ‎со- (so-) + ‎жить (žitʹ, “to live”) + ‎-тель (-telʹ) → ‎сожи́тель (sožítelʹ, “cohabitant”)