BIP39 Words Starting with Z (4 words)
The 4 BIP39 words that start with Z run from #2045 zebra to #2048 zoo in the English wordlist: indexes 2044 to 2047, or 11111111100 to 11111111111 in binary, so all of them begin with the bits 111111111. That is 0.2% of the 2048 words, the smallest letter group. In list order they are zebra, zero, zone and zoo, from 3 to 5 letters long.
No two of them share their first three letters, so three letters identify all 4; only two-letter beginnings repeat: "ze" (zebra and zero) and "zo" (zone and zoo).
Two of the 4 words have look-alikes one letter away: zero (hero) and zone (bone, one, ozone and tone). Read aloud, 6 pairs differ by a single sound, for example zone /zəʊn/ and loan /ləʊn/, own /əʊn/ or phone /fəʊn/. One of the words appears in the official BIP39 test vectors: zoo (vectors #4, #8 and #12).
All 4 BIP39 words starting with Z
Similar-looking words to check
These 5 pairs differ by one letter, with at least one word starting with Z. Both words are valid, so a slip between them passes the word check and only the checksum can catch it.