Etymology dictionary (including word roots; else a separate word roots dictionary).
Unabridged dictionary.
Optional: Picture dictionary.
Encyclopedia.
Categorized thesaurus
Optional: Rhyming dictionary.
A course for study could be embarked on from as early as sixteen.
For earlier learners: look into picture encyclopedias (sic; encyclopediae) & picture dictionaries.
For second language learners: look into bilingual picture dictionaries.
Thank you!
⸻ ValentynJoe
USAMinnesota
2024Maysub>6th