Answer:

tougher

Answer	Crossword Clue
TOUGHER	More durable
TOUGHER	Harder to chew
TOUGHER	More difficult to chew

TOUGHER	More difficult.
TOUGHER	Harder to crack
TOUGHER	Not so easy
TOUGHER	Harder to solve

Crossword

a puzzle consisting of a grid of squares and blanks into which words crossing vertically and horizontally are written according to clues.