Compare Strings In Two Workbooks

I have a workbook called Keyword that has two columns c,and d, of words.

The length of the columns can vary,because I add words to them.

I also have a workbook called testfile, and cell B1 has a word in it.

Testfile also has an .xla module that adds in when testfile is open.

I want to type a function called asset in cell C1 of Testfile,and have
it compare each word in Keyword workbook to the word that's in cell B1
of testfile. If a match is found in column C of Keyword, the function
returns the letter C. If match is found in col D of Keyword, it returns
the letter D. If no match, function returns "no match".

I have both workbooks open and the vba code I stuck at the bottom of
the .xla module as another function.

Here's my code so far.

Function asset(Description As Variant) As String 'arg. is the word in cell B1 in testfile

Dim LastRowOfC As Integer, LastRowOfD As Integer
Dim i As Integer