Etymologically connected words
Root: act (v,n)
actor (n), actress (n);
react (v), reactor (n), reactant (n);
action (n), reaction (n), reactionary (n,adj); inaction (n);
active (adj), reactive (adj), activity (n), reactivity (n);
..., ..., ...;
..., ..., ...;
interact (v), interaction (n), interactive (adj), interactively (adv).