1. not explained or able to be explained
Usage: often used in the phrase ‘unaccounted for’
2. missing and not found or located
Usage: typically used with ‘for’

Examples

• Several thousand dollars remain unaccounted for in the budget.
• Three passengers are still unaccounted for after the accident.
• The missing files are completely unaccounted for.
• Large amounts of inventory went unaccounted for during the audit.
• Two hikers remain unaccounted for despite the extensive search.
• The strange noise in the attic is still unaccounted for.