Useless synonyms include:

• worthless

• futile

• ineffective

• pointless

• valueless

• impractical

• unproductive

• ineffectual

• unusable

• unworkable

These words convey the idea of something having no practical use, value, or effectiveness. For example:

• "The plan was futile—it had no chance of success."

• "Her efforts were pointless; nothing changed."

• "The old tool is now useless and cannot be repaired."

For crossword puzzles, common 5-letter synonyms include vain, idle, null, or nugatory.