prosiopesis

noun1

1. •
   Ellipsis of the beginning of a grammatical construction, common in informal speech and spontaneous written electronic communication, frequently occurring in stock phrases and interjections.

   • The students of English were making good progress in getting to grips with the intricacies of informal constructions, peppering their conversations with proverbial idioms and substituting stock phrases like “Good morning!” and “Thank you.” with prosiopeses like “Morning!” and “‛Kyou.”