СУМ-20 (Academic Dictionary of Ukrainian)
The official 20-volume academic dictionary of Ukrainian, online and free.
What it actually is
Published by the Ukrainian Lingua-Information Foundation of the National Academy of Sciences, this is the authoritative monolingual dictionary — the one to cite when you need a definitive answer about a word's meaning or usage. Note that the widely-linked sum.in.ua is an unofficial copy of older volumes; this is the sanctioned, maintained edition. Entirely in Ukrainian and written for native-level users, so it is an advanced tool rather than a learning aid. Free to search.
What it covers
- Vocabulary
- Reading