[Agema]

The sarissa is a pike in most meaningful senses. The semantic difference has very little to do with tactics, function and form, and a lot to do with the fact the former fell out of use during late BC and the latter was a reintroduction centuries later. It's hard to agree with the design difference argument because there are notable differences in designs across the history of European pikes, yet they are all still pikes.

At least one encyclopaedia and some books on ancient warfare I've read readily describe the sarissa as a pike or a pike-like weapon, so I'd suggest expert opinion considers them effectively the same thing.