Meaning : The state of being inactive.
Synonyms : inaction, inactivity
The state of being active.
His sphere of activity.Meaning : A disposition to remain inactive or inert.
Example :
He had to overcome his inertia and get back to work.
Synonyms : inactivity, inertia
The trait of being active. Moving or acting rapidly and energetically.
The level of activity declines with age.