A pilot reported confusion about his clearance reroute from ZTL which included the words DIFFI ONE which he heard as Victor 51.

Narrative

I am sending this because of naming issue of an 'Arrival' which did not result in any problem or conflicts; but to make a recommendation on the naming of that arrival. I was on an IFR flight plan at 8;000 FT; about 50 miles south of Atlanta VOR (ATL) and outside the Class B. I was in contact with Atlanta Center and following a clearance of direct to my destination airport 4A4 (Polk County - Cedartown). ATC contacted me for a change in clearance. What I thought I heard was 'You are cleared to the NANCY Intersection; join V51; direct (4A4).' I had the ATC Controller spell out the intersection; which was really NANNC. I entered it in the GPS as he spelled it; and it found it immediately so and I replied with 'Cleared to NANNC (spelling it out); intercept V51; Direct'. The NANNC Intersection was approximately 40 miles away; so steered toward it. It was at night; so I started scanning my Enroute Chart to find the intersection and how it was going to intercept V51. I couldn't find either the intersection or V51 nearby (although I was familiar with the airway; but couldn't place where); even though my Garmin 530W clearly showed the intersection location with no problem. There was only about a couple of minutes after receiving this clearance; when the Controller came back and said that it wouldn't work; and would give a new one in a couple of minutes. I figured it was due the same problem I was having with V51. I suggested that after NANNC; go direct to 4A4; which he replied he was working on. About minute later; he gave me a new clearance 'After NANNC; direct 4A4.' This was no problem; so I ended my search V51. After the flight; I wanted to know why I couldn't find the intersection or V51 on my Enroute Maps right away. When that didn't work; I finally figured out that since the GPS found it; it must be on a STAR; SID or Approach Plate. It turned out that NANNC is a fix for the 'DIFFI ONE ARRIVAL' Atlanta arrival. I don't know why I thought I heard 'Victor'; but the DIFFI ONE; sounded like '51'; and I don't remember ever hearing the word 'Arrival' in the clearance. Interesting enough; I repeated the instructions as 'After NANNC Intersection; intercept V51; then direct'; which ATC Controller didn't catch the Victor or the missing word 'Arrival' either. I guess; by the book; I shouldn't have accepted the clearance until I found it on the map; or responded that I couldn't find it; but since I clearly had the intersection and almost 20 minutes to find V51; it wouldn't be a problem; and the ATC Controller didn't question my reply either. It was resolved so quickly; it became a non-issue. Bottom line; I think the name 'DIFFI One' sounds too close to '51'; which started and caused the confusion in the first place; so I would recommend that the name be changed. As a side note; on my side; reception of ATC radio was very clear; as was the Controller's speech. I had no problem understanding instructions. Thank You for your help.