Home in means to direct onto a target. The phrasal verb home in derives from the 19th-century use of homing pigeons, but today the term usually refers to missiles that home in on their targets. It’s also commonly used metaphorically.
Hone in derives from a mishearing of home in. The verb hone means to sharpen or to perfect, so hone in makes no sense.
Because the erroneous hone in is so common, it has appeared in dictionaries and is accepted as a variant of home in. Still, most edited publications prefer the original form. For example, these publications use home in:
Bone cancer is sometimes treated with radioactive isotopes that home in on the bone … [NY Times]
But they do reveal Dahl’s uncanny ability to home in on the darker reaches of human ingenuity. [Financial Times]
Producing a reliable high-speed, high-precision missile that can home in on a target in the atmosphere is extremely difficult. [Washington Post]
But hone in occasionally—for example:
And it helps him hone in on a smaller volume of applications. [Wall Street Journal]
I find that I instinctively hone in on what is necessary, forcing out time wasting as a result. [Evening Standard]
