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 requiring great exertion; laborious; difficult:an arduous undertaking. 2  requiring or using much energy and vigor; strenuous:making an arduous effort. 3  hard to climb; steep:an arduous path up the hill.  hard to endure; full of hardships; severe:an arduous winter.