AM and PM are associated with 12-hour timekeeping, as opposed to the international 24-hour clock. The 12-hour system grew up mainly in Northern Europe, and spread globally from there via the British Empire.
The adjective STRENUOUS has 2 senses: 1. characterized by or performed with much energy or force. 2. taxing to the utmost; testing powers of endurance. Familiarity information: STRENUOUS used as an adjective is rare.
1. Demanding great effort or labor; difficult: the arduous work of preparing a Dictionary of the English Language (Thomas Macaulay). 2. Testing severely the powers of endurance; strenuous: a long, arduous, and exhausting war. 3. Hard to traverse, climb, or surmount.