In a similar way to つまり
is another grammar pattern in Japanese that is often translated as ‘in other words’. It may also be translated as ‘namely’, or ‘that is to say’. While 即（すなわ）ち
is a 副詞（ふくし） (adverb), it is often used as a 接続詞（せつぞくし） (conjunction), linking two sentences via some sort of reasoning.
This person is my wife's mother. In other words, my mother in law.
I get paid for playing video games. In other words, I am a professional gamer.
The kanji used in 即（すなわ）ち
simply means ‘in concordance’. This shows that the nuance associated with 即（すなわ）ち
is that of ‘agreeance’ or ‘correspondence’ to something else, while つまり
is purely that of ‘summarisation’.
This car does not run anymore. In other words, it is a decommissioned car.
He is my father's brother. In other words, he is my uncle.