tensar  (una cuerda, etc.) - to tense, to make taut, to draw (a bow) 

apretar  (un nudo, un tornillo, etc.) - to press, to push, to press, to push (a button), to tighten, to fit tightly, to be too tight, to squeeze 

apretarse  (el cinturón)

reforzar  (las reglas) - to reinforce, to strengthen, (figurative) to beef up, to encourage, to support