The term 'BEAT FAST' can be broken down into two crossword solutions: RACE (4 letters) and THROB (5 letters). RACE is a verb meaning to compete in a contest of speed, usually involving running, swimming, or riding. It can also be used as a noun to refer to such a competition. THROB is a verb meaning to beat or pulsate rapidly and strongly, often in reference to the heart. It can also be used as a noun to refer to a strong, regular pulsation.