The following words are Bedspread Words™ because:
Using the standard number of tiles in a Scrabble set, a blank tile will be needed to write out the word.
Graph:
Proof:
Not Bedspread Words™ can be made with the standard Scrabble letter count.
ZIGZAGGING is a Double Bedspread Word™ because:
ZIGZAGGING (3 Gs and 1 Z in Scrabble, 1 blank tile for G, 1 blank tile for Z)...
Therefore, two blank (bedspread) tiles are needed).