Possible Clues:

• States of ___ (solid, liquid, gas, plasma)
• Be significant
• Stuff for which mother needs extra time
• Affair to be of consequence
• Physicist giving name to frequency shift
• 'Seems that's the trouble with rugger, perhaps (6)'
• Subject; be important
• Stuff — mean something
• Physics concern
• Blustering martinet drops in for material