Answer:

PRE

Answer	Crossword Clue
PRE	Amble start
PRE	Judicial start?
PRE	Historic introduction?

PRE	Historic starter
PRE	Law or school lead-in
PRE	Post opposite
PRE	Post's opposite
PRE	..-op
PRE	Prefix for vent or sent
PRE	Season lead-in
PRE	Fab start?

PRE	Post-'s opposite
PRE	Start to dominate?
PRE	..-Columbian era
PRE	Historic beginning?
PRE	Before
PRE	Beginning for sent or vent
PRE	..-med
PRE	"Before," when before

PRE	Lead-in to med or op
PRE	Opposite of post-
PRE	Before, when before
PRE	Ante- kin
PRE	Self-descriptive sort of fix?
PRE	Equal of ante-
PRE	Post- opposite
PRE	Prefix's prefix

PRE	Ante- alternative
PRE	...-K
PRE	Cautionary opening?
PRE	Season opener?
PRE	Cautionary beginning?
PRE	Disposition opener
PRE	Existing intro
PRE	Lead-in for law or med

PRE	Before, at the fore
PRE	Cambrian opening
PRE	Existing start
PRE	Historic leader?
PRE	Med lead-in

Crossword

a puzzle consisting of a grid of squares and blanks into which words crossing vertically and horizontally are written according to clues.