S: (n) matter (that which has mass and occupies space) "physicists study both the nature of matter and the forces which govern it"
S: (n) process, physical process (a sustained phenomenon or one marked by gradual changes through a series of states) "events now in process"; "the process of calcification begins later for boys than for girls"
S: (n) substance (material of a particular kind or constitution) "the immune response recognizes invading substances"