### Clue: Tense is misused primarily in stupid turn of phrase (5)
### Answer: IDIOM 
 ### Explanation: Definition: turn of phrase
 "t"(abbrev. for "tense") **replaced by**(is) **1st letter of**(… primarily) "misused" **in **"idiot"(stupid/form of address for a stupid person, as in "you're not listening, stupid").