beneficial
The definition for beneficial is "Helpful." Used in a sentence: there is no doubt that eating vegetables is beneficial to one's health.
compulsion
The definition for compulsion is "An irresistible impulse." Used in a sentence: Tamar, a shoe fanatic, could not resist the compulsion to buy the shiny red boots.
elate
The definition for elate is "To fill with joy." Used in a sentence: It elated Margaret to be awarded first place in the science fair.
flaw
The definition for flaw is "An imperfection." Used in a sentence: The otherwise perfect diamond had a tiny flaw that reduced its value.
retroactive
The definition for retroactive is "effective as of a prior time or condition." Used in a sentence: The retroactive law made even past infractions punishable.