### Clue: It helps to make 25 foul, we hear, after intensive publicity's curtailed? (6)
### Answer: HYPHEN 
 ### Explanation: Definition: It helps to make 25
  HEN{fowl,homophone(we hear) of "foul"} **placed after**(after) HYP(hype,intensive publicity without its last letter,curtailed)
Defn:  Answer to 25 across would "twentyone" or "twenty one" without it, so it does help.