Rigor is something strict, severe or demanding. 1  Harsh and strict treatment in the military for cadets is an example of rigor. 2  Freezing weather and ice are examples of the rigors of winter.  Difficult and challenging academic courses are an example of academic rigor.
The suffix gram means to draw or write. This is used in telegram.
For example, the prefix kilo-means 1000 times the original unit and the prefix milli-means 0.001 times the original unit. So one kilometre is 1000 metres and one milligram is a 1000th of a gram.