What is a Special PoS Word™?

_{This is in the spirit of the What is a Word™/Phrase™ series started by JLee with a special brand of Phrase™ and Word™ puzzles.}

If a word conforms to a certain rule, I call it a Special PoS Word™. Use the following examples to find the rule:

CSV version:

Special PoS Words™, Not Special PoS Word™
ADVICE, ADVERB
PRACTICE, PRACTICAL
DEVICE, DEMISE
LICENCE, LENIENT

Perhaps these are the only such words exist in standard English.

Also, as a bonus, provide a reasonable expansion for PoS.