Answer:

ESSENTIAL

Answer	Crossword Clue
ESSENTIAL	Absolutely necessary
ESSENTIAL	Needed
ESSENTIAL	Sine qua non

ESSENTIAL	Chief point
ESSENTIAL	Indispensible
ESSENTIAL	Must-have
ESSENTIAL	Necessary
ESSENTIAL	Not optional
ESSENTIAL	Requisite
ESSENTIAL	Key
ESSENTIAL	Highly important.

ESSENTIAL	Necessary.
ESSENTIAL	Required.
ESSENTIAL	Basic
ESSENTIAL	Intrinsic
ESSENTIAL	Hardly extraneous
ESSENTIAL	Necessary small bit of enzyme in saltine crackers (9)
ESSENTIAL	Hardly necessary
ESSENTIAL	Required

ESSENTIAL	Like many nutrients