One that condenses.
In optics, a lens or combination of lenses with a short focal length used for concentrating a light source onto a small area, as used in a slide projector or microscope substage lighting unit. A condenser can also be made using a concave mirror.
In electronic circuits, another name for a capacitor.
Laboratory apparatus used to condense vapors back to liquid so that the liquid can be recovered. It is used in distillation and in reactions where the liquid mixture can be kept boiling without the loss of solvent.