This is the 11739th most frequent French word.
sinon
"Sinon" means "if not" or "otherwise" in English.
In this sentence, 'sinon' is used to mean 'otherwise', presenting a consequence if the first condition ('leaving now') is not met.
Nous devons partir maintenant, sinon nous serons en retard.
We must leave now, otherwise we will be late.
In this sentence, 'sinon' is used to mean 'if not', suggesting an alternative possibility or option ('lawyer') to the first statement.
Je crois qu'il est médecin, sinon avocat.
I believe he is a doctor, if not a lawyer.
Here, 'sinon' is used to denote an alternative activity ('reading') when the primary condition or situation ('doing sports') does not occur.