Answer:

enigma

Answer	Crossword Clue
ENIGMA	"Hmmmmmm" provokeer
ENIGMA	Riddle
ENIGMA	Puzzle

ENIGMA	"Hmmmmmm" provoker
ENIGMA	Real poser
ENIGMA	Stumper
ENIGMA	Something inscrutable
ENIGMA	Baffler
ENIGMA	Poser
ENIGMA	Tough nut to crack
ENIGMA	Mystery

ENIGMA	Encryption machine of yore
ENIGMA	WWII cipher machine
ENIGMA	WWII coding machine
ENIGMA	Challenging riddle
ENIGMA	Conundrum
ENIGMA	Toughie
ENIGMA	Problem
ENIGMA	Baffling problem

ENIGMA	Puzzling problem
ENIGMA	Riddle relative
ENIGMA	World War II encoding machine
ENIGMA	Brainteaser
ENIGMA	Puzzler
ENIGMA	It's puzzling
ENIGMA	Something of a mystery
ENIGMA	It's something of a mystery

ENIGMA	Mona Lisa's smile, for one
ENIGMA	Inscrutable sort
ENIGMA	It's hard to understand
ENIGMA	Puzzling person
ENIGMA	Puzzling situation
ENIGMA	Something hard to grasp
ENIGMA	Brain twister
ENIGMA	Puzzlement

ENIGMA	Head-scratcher
ENIGMA	" .. Variations": Elgar opus
ENIGMA	Perplexing puzzle
ENIGMA	It's a mystery
ENIGMA	Perplexity