Without seeing the entire coin, it's hard to tell what might be going on with your coin. FULL IMAGE photos, obverse and reverse, are helpful.
Nickels always have weighed 5.0 grams with 25% nickel and 75% copper. As Paddy mentioned there is a range of tolerance that is acceptable. The tolerance is: ± 0.194 grams which would range from 4.8-5.2. However being 4.6 is not enough to make it worth anything and we don't know if your coin was subjected to acid which would eat away some of the weight. Sometimes a sheet that is rolled to make planchets can be rolled a little too thinly and the coins will be light. (Or the opposite.) Ideally, if the coin was minted on a slightly smaller, slightly lighter foreign planchet, then you actually have something. This is why good photos of both sides can help people see what you might have. All things being equal, it's a nickel. But you never know.
On the other end of the spectrum - Don't forget about the counterfeit Henning nickels, which weighed 5.4 grams, and were minted in 1939, 1944, 1946, 1947, and 1953.
Yes but some of those years the majority of coins were dumped in the river. I don't think they were recovered. I think the 39 and the 44 are the most common. They run heavy and the details are very mushy. The 44 has no MM over the dome, and most of the 39's have that bad R in Pluribus. This is what the ANA site says: Some 1939 and 1944 Henning nickels also have a die crack extending from the US in PLURIBUS to the dome of Monticello. 1944 is the most common date. In 1954, he placed into circulation an estimated 100,000 counterfeit nickels into circulation. After learning the authorities were on his tail, Henning dumped his remaining 400,000 nickels into Cooper Creek and the Schuylkill River. I was trying to find which dates are the rare ones.
