They started as same word, but their meanings have drifted apart over time.
We'll tell you all the perpendiculars
We're intent on clearing it up
We're gonna stop you right there
'Poets laureate'? 'Court-martials'? The curious history of postpositive adjectives in English.
Why don't they call it the Merriam-Webster comma?
Thawing one of the mysteries of English