catch cold

catch cold  {v. phr.}

1. or take cold

To get a common cold-weather sickness that causes a running nose, sneezing, and sometimes sore throat and fever or other symptoms.

Don't get your feet wet or you'll catch cold.

2.  {informal}

To catch unprepared or not ready for a question or unexpected happening.

I had not studied my lesson carefully, and the teacher's question caught me cold.