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.
If something is tenuous it's thin, either literally or metaphorically. If you try to learn a complicated mathematical concept by cramming for 45 minutes, you will have a tenuous grasp of that concept, at best. Tenuous comes from the Latin word tenuis, for thin, and is related to our word tender. Something can be physically tenuous, like a spiderweb or ice on a pond. We more often use it in a metaphorical sense, to talk about weak ideas. Tenuous arguments won't win any debate tournaments.