1. Operation on something past or preceding 
2. Action returned, or action backward

Derived forms: retroactions

• dronabinol
• drone
• drone on
• drone pipe
• drongo
• droning
• drool
• drool over
• drooler
• droop
• drooping
• drooping brome
• drooping juniper
• droopingly
• droopy
• drop
• drop a line
• drop anchor
• drop arch
• drop away
• drop back
• drop behind
• drop biscuit
• drop by
• drop by the wayside