“a four-year-old boy”
synonyms: lad, schoolboy, child, little one, young one, youngster, youth, young man, young fellow, young adult, young person, teenager, adolescent, juvenile, minor, junior; More
antonyms: man
a person’s son.
“she put her little boy to bed”
a male child or young man who does a specified job.
“a delivery boy”

2.a man, especially a young or relatively young one.
“I was the new boy at the office”
informal
men who mix socially or who belong to a particular group, team, or profession.
“I hope that our boys will continue to play good quality rugby”
dated
a friendly form of address from one man to another, especially from an older man to a young man.
“my dear boy, don’t say another word!”
datedoffensive
a black male servant or worker (often used as a form of address).
a form of address to a male dog.
“down boy!”