Why 2048 words
Each word stands for an 11-bit number, and 211 = 2048. The mnemonic is the entropy plus checksum written 11 bits at a time. That is also why the list order matters: word 0 is always abandon and word 2047 is always zoo.
How the English list was designed
- Unique first four letters — every word can be identified from its first four letters.
- No very similar words — pairs such as build/built were avoided to reduce mistakes.
- Sorted alphabetically — so a word can be found quickly and its index looked up.
- Common, short words — 3 to 8 letters.
Word order and the checksum
Picking any 12 words from the list does not make a valid mnemonic. The final word includes checksum bits calculated from the others, so for 12 words only 128 of the 2048 words fit in the last position. See how the checksum is calculated.
Languages and compatibility
The same entropy produces different words in each language’s list, and the seed is derived from the words themselves. A Spanish mnemonic entered into a wallet expecting English will fail or restore a different wallet. Most wallets support English only.