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There are only two terminals on the device, so I'd assume it to be a trimmer cap.
Most trimmer pots have three terminals, although you can find some from the 1960's (e.g., those used in a Simpson 260 Series 5 VOM) that had only two leads and were used in the configuration of a rheostat -- nothing more than a variable resistance vs. a potentiometer. But these days, you just don't see those 2-terminal resistors anymore.
Thought I'd throw those thoughts in since the posts never really did nail down that it was one device or the other. You know, a quick check with an ohmmeter across the leads will provide you with the definitive answer: an open means it's a variable cap (or a defective pot!) while a resistance will assure you that it's a variable resistor and turning the adjustment should change the value.