Noun
English Wikipedia has an article on:tensionerWikipedia
tensioner (plural tensioners)
Any device that maintains or applies tension
Also, if this belt is replaced around 105,000 miles, it is a good idea to change the water pump, thermostat, belt tensioner and all the idler pulleys for this belt. Source: Internet
The 944S featured a high performance normally aspirated, dual-overhead-cam 16-valve convert version of the 2.5 L engine (M44/40) featuring a self-adjusting timing belt tensioner. Source: Internet