copepod, copepod crustacean - minute marine or freshwater crustaceans usually having six pairs of limbs on the thorax; some abundant in plankton and others parasitic on fish mussel shrimp, ostracod, seed shrimp - tiny marine and freshwater crustaceans with a shrimp-like body enclosed in a bivalve shell
time and a half(noun) a rate of pay that is 1.5 times the regular rate; for overtime work.
In particular then, the half life of a radioactive element is the time required for half of it to decay (i.e. change into another element, called the daughter element). So if a radioactive element has a half life of one hour, this means that half of it will decay in one hour.