If a phrase adheres to a certain rule, then I call it a Stair Word™.
Use the examples below to find the rule.
In case you want it in CSV:
Stair Words™, Not Stair Words™ PANAMA, AFRICA SOUPY, SOLID WICKER, WACKER INLET, OUTLET WAIF, LADY ENCHANT, IMPRESS BORN, BARN SIGN, SINE QUALM, QUILT BICKER, ARGUE FARADAY, EINSTEIN CALM, STORMY FOULER, VULGAR BANANA, ORANGE MANAGE, GOVERN BUCKET, PITCHER
The puzzle relies on the series' inbuilt assumption, that each wordcan be tested for whether it is a Stair Word™ or not on its own.