Answer:

erst

Answer	Crossword Clue
ERST	Formerly, formerly
ERST	Former, formerly
ERST	Formerly formerly

ERST	Once, once
ERST	Once, upon a time
ERST	Prefix for while
ERST	At one time, at one time
ERST	Early earlier
ERST	While opener
ERST	While opening
ERST	While opening?

ERST	Whilom
ERST	Archaic "formerly"
ERST	Formerly, old-style
ERST	Formerly, in olden days
ERST	Old-style "formerly"
ERST	Before a while?
ERST	Once, once upon a time
ERST	Prefix with "while"

ERST	While lead-in
ERST	"...which .. was irksome to me": "As You Like It"
ERST	At an earlier time, earlier
ERST	Old-style "once"
ERST	Previously, once
ERST	While beginning
ERST	While starter
ERST	Archaic adverb

ERST	Once before?
ERST	While beginning?
ERST	Before now, before now
ERST	Formerly, once
ERST	"... which .. was irksome to me": Shakespeare
ERST	"The even mead, that .. brought sweetly forth - The freckled cowslip": "Henry V"
ERST	Before, before
ERST	Once, at one time

ERST	Once, long ago
ERST	Previously, old-style
ERST	Formerly, previously
ERST	Aforetime
ERST	At one time, once