http://www.denialville.com/water-faucet-aerators/
What would cause low pressure in a faucet besides a clogged aerator?
I took off the aerator to clean it, and the water still had low pressure (though I suppose I don't know exactly what the flow should be like once the aerator is off; but it seemed weak to me). I cleaned the aerator and put it back on but there was no improvement.
there could be debris stuck in the stem
there could be insufficient water coming in at the valve under the sink
if it's only at that faucet, i recommend removing the supply line from the valve feeding the faucet under the sink, open the valve and see how much water comes from there as a starting point.