Answer:

harder

Answer	Crossword Clue
HARDER	"Work smarter, not .."
HARDER	Less cushiony
HARDER	Higher on the Mohs scale

HARDER	More puzzling
HARDER	More demanding
HARDER	More challenging
HARDER	Like a Sunday crossword compared to a Monday one
HARDER	Less of a picnic
HARDER	More difficult
HARDER	Less simple
HARDER	"... the ... they fall"

HARDER	More difficult.
HARDER	More enduring.
HARDER	More arduous.
HARDER	More rigorous.
HARDER	More oppressive.
HARDER	More steely
HARDER	More knotty
HARDER	More trying

HARDER	More unyielding
HARDER	More callous
HARDER	Less giving
HARDER	Less lenient
HARDER	Not so easy
HARDER	" . . . the ... they fall"
HARDER	"Pull more!"
HARDER	Taskmaster's cry

HARDER	Weather indicator
HARDER	More rigorous
HARDER	More puzzling, as a crossword
HARDER	Like topaz vis- -vis quartz