From the given options, choose a word with the meaning opposite to 'S…

The word "sibling" refers to a brother or sister.

Option 1: "Offspring" refers to the child or children of a person or animal. It is the opposite of "sibling" because it refers to the next generation rather than a brother or sister.

Option 2: "Country" refers to a nation or a geographical region and is not the opposite of "sibling."

Option 3: "Class" typically refers to a group of students or a category and is not the opposite of "sibling."

Option 4: "Mountain" is a geographical feature and is not the opposite of "sibling."

So, the word with the meaning opposite to "sibling" is "Offspring" (Option 1).