lose (one's) tongueTo lose the capacity to speak, as from shock
[TahlilGaran] Dictionary of Contemporary English ▲
lose one's tongue v. phr., informal To be so embarrassed or surprised that you cannot talk.
The man would always lose his tongue when he was introduced to new people. Compare: CAT GET ONE'S TONGUE.
[TahlilGaran] English Idioms Dictionary ▲