Puerile (pyoor’ al or pyoor’ile) - from the Latin “puer” meaning boy.
Definition: Childish; silly; immature; trivial.
Use this word in a sentence: “Donald Trump is the very definition of puerile.”
I’ve always loved this word — it’s a bit unusual, but it really is an excellent word to describe an immature person. And I am a nerd and loved Latin class.
I’ve rarely had a chance to use it during my lifetime, but have had numerous opportunities to use it during the past year, as in, “God, that man is so puerile!!!”