They started as same word, but their meanings have drifted apart over time.
Why don't they call it the Merriam-Webster comma?
'Poets laureate'? 'Court-martials'? The curious history of postpositive adjectives in English.
Head, shoulders, metaphors, and toes
The awkward case of 'his or her'
And who put it there, anyway?
English was never the same after the Norman Conquest