shibboleth /shibˈə-leth/

1. The criterion, catchword or catchphrase of a group, party or sect by which members may be identified
2. A slogan
3. A peculiarity of speech
4. The Gileadite test-word to distinguish an Ephraimite, who could not pronounce sh (from Bible, Judges 12.5–6)
5. Any such test

• double take
• double takes
• double-talk
• doublethink
• doublethinks
• double-threaded screw
• double-threaded screws
• double time
• doubleton
• double-tongue
• double-tongued
• double-tongues
• double-tonguing
• doubletons
• double top
• doubletree
• doubletrees
• doublets
• double-u
• double up
• double vision
• double wedding
• double weddings
• double whammy
• double witching