Tuck tail is an idiom that typically means to retreat or show fear. There are a variety of synonyms for this phrase, each with their own unique connotations. One common synonym for tuck tail is "run away", which implies a hasty exit or escape from danger. Another option might be "back down", which suggests a more strategic retreat or the decision to give up on a confrontation. Other synonyms for tuck tail might include "withdraw", "flee", "retreat", "recoil", or even "cower". Ultimately, the choice of synonym will depend on the context and severity of the situation at hand.