Walk through Amos, verse by verse, with the great Bible Commentaries of Matthew Henry (1662 - 1714) & Adam Clarke (1760 - 1832)
8:10
And I will turn your feasts into mourning, and all your songs into lamentation; and I will bring up sackcloth upon all loins, and baldness upon every head; and I will make it as the mourning of an only son, and the end thereof as a bitter day. KJV
{And I shall convert your feast days into mourning, and all your songs into wailing; and I shall bring
in on each back of you a sackcloth, and on each head of you baldness; and I shall put it as the mourning of [an] one begotten son, and the last things thereof as a bitter day.}Wycliffe's Bible
A bitter day - A time of grievous calamity.