fossil

"fossil" is the #736 word in the official BIP39 English mnemonic wordlist. It is encoded as the 11-bit binary value 01011011111 (decimal index 735), placing it at the 36% mark of the full 2048-word list.

The 4-letter prefix "foss" uniquely identifies this word among all 2048 entries. At 6 characters, it falls in the typical length range for BIP39 words, balancing readability with distinctiveness during manual wallet recovery.

Located in the middle section of the wordlist (index 735), "fossil" belongs to the "F" letter group, which contains 106 words. It is the #85 entry in that group. Mid-range words have a balanced mix of 0s and 1s in their binary representation.

In a 12-word seed phrase, each word encodes 11 bits of entropy. The probability of "fossil" appearing in any specific position of a randomly generated phrase is 1 in 2048 (≈ 0.049%). A complete 24-word phrase encodes 256 bits of entropy, providing security equivalent to a key space of approximately 1.16 × 10⁷⁷ — far beyond the reach of brute-force attacks.