slacken

In the 1990s, his pace began to slacken, and eventually the hits evaporated.
Are We in the Midst of a Kevin Costner Comeback?|Andrew Romano|January 28, 2014|DAILY BEAST
The liner began to slacken her speed, and the tugboat soon was alongside.
Sinking of the Titanic|Various
The march was resumed after a short delay, and not until two hours had passed did the Indian so much as slacken his pace.
The Search for the Silver City|James Otis
Though ordinarily surefooted, Merlin stumbled frequently, and Richard was obliged to slacken his pace.
The Lancashire Witches|William Harrison Ainsworth

I never saw such a runner; not a bit does he slacken for the hill—and what bright cheeks and eyes!
The Young Step-Mother|Charlotte M. Yonge
No horses had passed recently upon them, and he did not slacken his pace to examine them.
The White Chief|Mayne Reid

British Dictionary definitions for slacken

slacken

/ (ˈslækən) /

verb (often foll by off)

to make or become looser

to make or become slower, less intense, etc

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012