a.

1. 严格的；严厉的；苛刻的
   These soldiers have to undergo very rigorous trainings before they become frogmen.

   这些兵在成为蛙人之前都必须经过非常严峻的训练。

2. 严酷的；严峻的
3. 精确的；严密的
   He made a rigorous study of the plants in the area.

   他对该地的植物进行了慎密的研究。

adj.

1. extremely thorough, exhaustive, or accurate.
2. (of a rule, system, etc.) strictly applied or adhered to.
   ▸adhering strictly to a belief or system.
3. harsh and demanding.