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

Derived forms: retroactions

• Gruidae
• Gruiformes
• grumble
• grumbler
• grumbling
• grumbly
• grume
• grummet
• grumose
• grumous
• grump
• grumpily
• grumpiness
• grumpy
• Grundyism
• grunge
• grungily
• grungy
• grunion
• grunt
• grunt-hoot
• grunter
• gruntle
• Grus
• Grus americana