With
Sheet2 containing this list in A1:B6
a	small
A	big
w	small
W	big
Q	big
s	small
and...Sheet1 containing this list in A1:A8
a
A
w
W
q
q
s
Q
This formula returns the category (from Sheet2) that corresponds
to the letter in Col_A
B1: =IF(ISNUMBER(MATCH(1,INDEX(--EXACT(A1,
Sheet2!$A$1:$A$6),0),0)),MATCH(1,INDEX(--EXACT(
A1,Sheet2!$A$1:$A$6),0),0),"No Match")
Copy that formula down through B8.

Is that something you can work with?