Modifiers matching duck:

• small,
• jealous,
• short-tempered,
• tenacious,
• aggressive,
• insecure,
• common,
• indigenous,
• determined,
• paranoid,
• unusual,
• wild,
• optimistic,
• slobbery,
• larger,
• marine,
• bullying,
• large,
• zany,
• boastful,
• lisping,
• daffy,
• native,
• here,
• brash,
• pushy,
• breeding,
• rare,
• smaller,
• domestic,

Simple categories matching aggressive:

• person,
• warrior,
• vegetable,
• predator,
• fluid,
• action,
• acid,
• thug,
• duck,
• womanizer,
• enzyme,
• feeder,
• intervention,
• businessman,
• hero,
• pet,
• equine,
• cowboy,
• terrorist,
• comedian,
• tycoon,
• interference,
• creature,
• conflict,
• ceo,
• liquid,
• shrub,
• hunter,
• outlet,
• tumor,
• nature,
• bully,
• tyrant,
• cop,
• politician,
• billionaire,
• president,
• solution,
• cargo,
• agent,
• activity,
• native,
• scientist,
• detective,
• disease,
• illness,
• invertebrate,
• hacker,
• offense,
• pest,
• prey,
• neoplasm,
• monster,
• option,
• campaigner,
• therapy,
• malignancy,
• offence,
• dissident,
• encounter,
• actor,
• form,
• superhero,
• compound,
• pioneer,
• investor,
• track,
• chemical,
• lesion,
• change,
• outdoorsman,
• substance,
• cancer,
• ant,
• environment,
• act,
• grass,
• medium,
• chef,
• spy,
• dog,
• adventurer,
• tetra,
• cichlid,
• crooner,
• athletics,
• behaviour,
• caveman,
• dictator,
• ion,
• care,
• bass,
• cleaners,
• demon,
• placental,
• tree,
• lymphoma,
• humorist,
• treatment,
• event,
• athlete,
• motive,
• behavior,
• activist,
• solvent,
• game,
• material,
• bird,
• sport,
• beast,
• measure,
• fish,
• villain,
• gas,
• socialization,
• interaction,
• lady,
• father,
• singer,
• emotion,
• conqueror,
• animal,
• child,
• sportsman,
• condition,
• emperor,
• crime,
• component,
• insect,
• explorer,
• soldier,
• king,
• boxer,
• mayor,
• plant,
• policeman,
• reagent,