What is the singular possessive of the word compass?

Answer 1

There are two accepted forms for possessive singular nouns ending in s:

Add an apostrophe (') after the existing s at the end of the word: compass'

Add an apostrophe s ('s) after the existing s at the end of the word: compass's

Example:

The compass' case is polished brass.

The compass's case is polished brass.

Answer 2

The singular possessive form of "compass" is "compass's" or "compass'."