a figment of (your) imagination

something created by your mind.

I thought I saw someone standing in the shadows, but it was just a figment of my imagination.

• keep powder dry
• keep quiet
• keep quiet about
• keep quiet about something
• keep shirt on
• Keep shirt on!
• keep someone at arm's length
• keep someone at bay
• keep someone company
• keep someone down
• keep someone guessing
• keep someone in check
• keep someone in mind
• keep someone in the dark
• keep someone in the picture
• keep someone on a short leash
• keep someone on a tight leash
• keep someone on the edge of seat
• keep someone on the edge of their seat
• keep someone on their toes
• keep someone on toes
• keep someone posted
• keep someone sweet
• keep someone up
• keep someone up to date