motiveless

/ˈmoʊtɪvləs/
adjective
  1. Having no apparent reason or cause; without a motive.
    • She committed a motiveless act of kindness, expecting nothing in return.
    • The crime seemed motiveless and confused the detectives.
    • His motiveless anger surprised everyone in the room.
Antonyms
What does "motiveless" mean? | whatsthatwordmean | whatsthatwordmean