This pill sounds like DILAUDID 4 MG
Generic Name
Hydromorphone
Description round, yellow, debossed with the Abbott logo (a) on one side and the number 4 on the opposite side
You will find an image at the bottom of the PDR page at
http://www.drugs.com/PDR/Dilaudid_Tablets.html
Info at
http://dilaudid.drugs.com