if you have a lookup field, its Html source is depicted as:
<option value="79" title="G0058">G0058</option>
I could use jquery to change the title from G0058 to company1 (field name: description) but I wonder if you can do this OOTB.
I would think the easiest way would be to edit the field settings through the UI and switch the "In this column" select to your Description field of the source list.
The resulting html in this case would be
<option value="79" title="company1">company1</option>