If you can, measure it's capacitance?
If you have access to a capacitance meter function, measure it's capacitance.
If just a VOM/DMM is available, use it in Resistance range. You should get no reading in any resistance range. Remember to also test by reversing the DMM leads for a second measurement, in case the line on the part is a diode's cathode?
If you suspect it's a diode, again go to the Ohm range around 2K to 20K. If it conducts with the neg/black lead hooked onto the part's polarity line, it is a diode. Different story in that case. If you get the same resistance value, even if you change ranges, then it looks resistive or a resistor.