Answer:

deadest

Answer	Crossword Clue
DEADEST	Least vivacious
DEADEST	Least sensitive
DEADEST	Least bouncy, as a tennis ball

DEADEST	Least lively.
DEADEST	Most insensitive
DEADEST	Least exciting
DEADEST	Least stimulating
DEADEST	Least hopping
DEADEST	Least bustling, as a part of town
DEADEST	Least active
DEADEST	Least lively

DEADEST	Least happening