It looks a lot like an older axe. Unlike a heavy modern axe head, the old pattern makes the most use of iron in the critical places- a long cutting edge, small eye- to save metal. But having a hammerhead, a poll, on the other side indicates it was used for driving as well. If it was an adze, that would be for driving pegs. But it's quite big. And it's not big because it's been "mushroomed" with use, It looks like it was made that way.

It could be just a very old pattern ( if it's been in seawater for a long time, you'd expect it to be more eroded). Maybe Greek or Italian farmers always used axes that looked like that ( the French have kept a hammer pattern for the past 200 years that doesn't have a claw for pulling nails) . Other than showing it to an old Greek or Italian farmer and asking, you might be able to date it somewhat by getting some of the rust off it. If it's an old axe ( like , 18th c. or earlier) the body of the axe will be iron and only part , the front edge, will be steel. There will be an obvious difference in how the two are corroded, showing an obvious weld. If the corrosion is uniform, it's likely much more recent.

EDIT actually, if the whole thing is soft, won't take and hold an edge, it's possible you've got something that's just for decoration, or the theater.