The "Hello" singer played dress up to virtually become the iconic country star -- blonde wig, pantsuit, and lots of cleavage ... while clutching a guitar.

Adele gave Dolly major props with the caption ... "The effortless queen of song, Dolly Parton! We love you! We wish We could possess an ounce of your ability."

Unclear why exactly Adele's shouting her out right now -- although it was Dolly's birthday a little over a week ago. Whatever the occasion ... it caught Dolly's attention.

She responded to Adele's post with some love, saying ... "And I will always love you!"

Yes, that's Dolly's.