expectorant
An expectorant helps you bring mucus up and out, the way loosening and flushing a partly blocked drain clears it. It is meant to make a chesty, productive cough more effective at clearing phlegm rather than to stop the cough.
The classic expectorant guaifenesin is thought to increase the volume and reduce the stickiness of airway secretions, making them easier to expel by coughing; older agents act partly by gently irritating the stomach to reflexly increase airway fluid. This is a different goal from a mucolytic, which chemically breaks down mucus, and the opposite goal from an antitussive, which suppresses the cough — combining a cough suppressant with an expectorant is generally illogical.
The evidence that expectorants meaningfully outperform simple measures is weak, and they are not recommended in young children. For most chesty coughs, plenty of fluids, warm drinks and time do much of the work, and a productive cough is usually the body clearing secretions and need not be suppressed.
An adult with a chesty cough takes a guaifenesin syrup to help loosen and clear the phlegm.
Guaifenesin is intended to make secretions easier to cough up, not to suppress the cough.
It rarely makes sense to combine an expectorant with a cough suppressant: one tries to bring mucus up, the other tries to stop the cough that does so.