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.
The abbreviation for gram is g. Milligram is a unit of mass in metric system and it is mostly used in medicine and pharmacy. There are 1 000 000 (one million) mg in 1 kg (1000 grams in 1 kg * 1000 mg in 1 gram = 1 000 000).