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.
Not easy to do, achieve, or master: 1  arduous, backbreaking, burdensome, demanding, effortful, exacting, exigent, formidable, hard, heavy, laborious, onerous, oppressive, rigorous, rough, severe, taxing, tough, trying, weighty. 2  See heavy.