Fit
What it really means
In British slang, "fit" usually means physically attractive, not just healthy or sporty. "He's well fit" = he is very good-looking. Context tells you which meaning is intended.
Context, tips & common mistakes
In casual British speech, especially among younger people, fit means physically attractive — 'he's well fit', 'she's fit' — which blindsides learners who know only the gym meaning. Context and tone separate the two: 'keeping fit' is exercise; 'your mate's fit' is not a fitness assessment.
Deployment rules: it is a peer-group compliment, fine among friends, out of place at work (commenting on a colleague's attractiveness is a different problem entirely), and slightly dated-sounding to some Gen Z ears who might say 'peng' or other regional variants instead. If someone calls you fit, it is straightforwardly flattering; a modest 'ha, cheers' is the native response.