apretar
to tighten
press
to press
+
-ar
verb suffix
Apretar means to tighten and can be thought of as related to press0 (as in pressing something tight) + -ar1 (verb suffix1).
verb
  1. to tighten
    To squeeze or press firmly
    Necesitas apretar más el tornillo. // You need to tighten the screw more.