deft ships the entire English Wiktionary (~1.1M words) on-device. the raw Wiktionary dump is ~18GB of JSONL — i stripped it down to just the basics (glosses, parts of speech, related words) and compressed it into a ~220MB SQLite database for definitions and a ~34MB Tantivy search index. next release should bring the total size down to ~100MB, just finalizing that.
search runs three tiers via Rust: full-text search through Tantivy, prefix match via SQLite LIKE sorted by word length, then fuzzy match with 2-char edit distance. results get deduplicated and merged. fast enough for search-as-you-type.
there's also OCR. you can point your camera at a page and tap words to look them up. useful for getting a defintion when books and gradually saving words without breaking focus.
flashcards use FSRS (Free Spaced Repetition Scheduler) through ts-fsrs. nothing fancy, just enough to make words stick.
works entirely offline, no account needed. iOS only right now.