Sentence:  Note that though the ideal gas itself contains no additional energy , the compressed <WSD>gas</WSD> does exert an increased pressure . 
Meaning of the word marked with <WSD> tags:  the state of matter distinguished from the solid and liquid states by: relatively low density and viscosity; relatively great expansion and contraction with changes in pressure and temperature; the ability to diffuse readily; and the spontaneous tendency to become distributed uniformly throughout any container