exercising caution or showing care or attention
"they were careful when crossing the busy street"
"be careful to keep her shoes clean"
"did very careful research"
"careful art restorers"
"careful of the rights of others"
"careful about one's behavior"
unhurried and with care and dignity
"walking at the same measured pace"
"with all deliberate speed"
Taking care; attentive to potential danger, error or harm; cautious.
"Before crossing the icy bridge, she moved very carefully to avoid slipping on the frozen surface."
In plain English: Careful means paying close attention to avoid making mistakes or getting hurt.
"Please be careful when crossing the street."
Usage: Use "careful" to describe someone who acts with caution to avoid mistakes or danger, such as being careful when crossing the street. It modifies the person's behavior rather than the object they are handling.
The word comes from Old English and originally meant full of care. It traveled into English through Middle English with the same meaning it holds today.