threadbare - wytarty, przetarty, wyświechtany, oklepany, złachmaniony, zużyty, sfatygowany, przechodzony, wysłużony, znoszony, wyszmelcowany, zeszmacony, złachany,
ostentatious- ostentacyjny, pretensjonalny, demonstracyjny, jawny, nieskrywany, nieukrywany, manifestacyjny, rozpoznawalny, dostrzegalny, odkryty, widoczny, widzialny, odczuwalny, wyeksponowany
melifluous - do you mean mellifluous?
melodyjny, śpiewny
strict - surowy, ostry, wymagający, ortodoksyjny, ścisły, bezwzględny, całkowity
These are just examples, many more are possible depending on the context.
Anyway, Lyzko, as a linguist you are probably very well aware that even if there existed a natural language consisting of 100 words only, the speakers od that language would invent other ways to convey myriads of meanings - it could be through syntax, word order, intonation, suffixes, subtle phoneme changes and so on. The number of words is just one of the factors operating within a language. Just look at the Polish and English verbs, Polish has more verbs but English has more tenses, we need a separate verb where you just use an appropriate tense, these things operate interchangeably between languages.
From my classes in linguistics I seem to remember that all natural languages are equally capable to fully describe the speakers' world, but they obtain this end by different means, so arguing about the number of words is dangerously close to a p*ssing contest.