When is 系 pronounced xì/xi and when is it pronounced jì？ A commonly used phrase is 没关系 (méiguānxi) which means "it doesn't matter"; it's used respond to 谢谢 (thank you) and 对不起 (sorry).

I found in this question that 系 can also be pronounced jì, as in 系好安全带 (jìhǎo ānquándài) meaning "fasten your seatbelt".

This means 系 is a 多音字 (duō yīnzì) or a heteronym (multiple pronunciation word).

Question: When is 系 pronounced xì/xi and when is it pronounced jì？

Doing a bit of Googling, I find:


中文系 = Zhōngwén xì (Chinese department)
太阳系 = tài yáng xì (solar system)
系统 = xì tǒng (system)
联系 = lián xì (to contact)


It looks like xì/xi is the default pronunciation.  I didn't find much with jì, except possibly 系好鞋带 (jìhǎo xiédài) = "tie your shoes".
I think you already got it.  

Most of time, it's pronounced as xì/xi 系. When pronounced as（jì）, it means 'fasten' and 'tie'.  系安全带. and 系鞋带. are good examples.