S: (n) rate (a magnitude or frequency relative to a time unit) "they traveled at a rate of 55 miles per hour"; "the rate of change was faster than expected"
S: (n) flux (the rate of flow of energy or particles across a given surface)
S: (n) frequency, frequence, oftenness (the number of occurrences within a given time period) "the frequency of modulation was 40 cycles per second"; "the frequency of his seizures increased as he grew older"