Answer:

past

Answer	Crossword Clue
PAST	History
PAST	Time gone by
PAST	Over and done with

PAST	Over and done
PAST	Checkered thing, maybe
PAST	Days of yore
PAST	Gone by
PAST	Over
PAST	Water under the bridge
PAST	Done and gone
PAST	Proust's "Remembrance of Things ..."

PAST	Bygone
PAST	Former
PAST	Nostalgic time
PAST	It's history
PAST	Time you can't relive
PAST	Bygone days
PAST	Previous
PAST	What was

PAST	Proust's "Remembrance of Things .."
PAST	Tense period?
PAST	Tense time?
PAST	It's behind us
PAST	Finished
PAST	Former time
PAST	Gone
PAST	Yesterday's tense

PAST	Where time travelers may go
PAST	Nostalgic concern
PAST	Time traveler's destination
PAST	After the hour
PAST	Historian's interest
PAST	Not present or future
PAST	Kind of tense
PAST	"Back to the Future" destination

PAST	"Living in the ..." (Jethro Tull song)
PAST	Existing only in memory
PAST	Personal history
PAST	"What's ... is prologue" (Antonio in "The Tempest")
PAST	Gone by, as time