index vs indexical

index is a noun but indexical is not a noun.

Word	Noun	Adjective	Verb	Adverb
index	Yes	No	Yes	No
indexical	No	Yes	No	No

index (noun)	indexical (noun)
the finger next to the thumb
an alphabetical listing of names and topics along with page numbers where they are discussed
a number or ratio (a value on a scale of measurement) derived from a series of observed facts; can reveal relative changes as a function of time
a mathematical notation indicating the number of times a quantity is multiplied by itself
a numerical scale used to compare variables with one another or with some reference number

index (adjective)	indexical (adjective)
	of or relating to or serving as an index