lengthener

From lengthen +‎ -er.

lengthener (plural lengtheners)

1. A person or thing that lengthens something

   This exercise is a great leg lengthener.

   I went to the store to get some eyelash lengtheners.

   • 1877, George Edwin Waring, Waring's Book of the Farm‎^[1], page 325:

     RYE is the great lengthener of the seasons.

• extender

• shortener

• relengthen