having the capacity for thought and reason especially to a high degree
"is there intelligent life in the universe?"
"an intelligent question"
exercising or showing good judgment
"healthy scepticism"
"a healthy fear of rattlesnakes"
"the healthy attitude of French laws"
"healthy relations between labor and management"
"an intelligent solution"
"a sound approach to the problem"
"sound advice"
"no sound explanation for his decision"
endowed with the capacity to reason
"The dog's intelligent behavior of opening the latch proved it could understand cause and effect rather than just reacting on impulse."
Of high or especially quick cognitive capacity, bright.
"After reading just a few pages of that dense textbook, it became clear she was an incredibly intelligent student who grasped complex concepts instantly."
In plain English: Intelligent means having a sharp mind and being very good at learning new things quickly.
"She is an intelligent student who always asks thoughtful questions in class."
Usage: Use "intelligent" to describe someone who possesses high mental ability and learns quickly. Do not use it to mean merely smart-alecky or well-informed without deep understanding.
The word "intelligent" comes from the Middle French term intelligent, which was derived from the Latin intellegēns. This Latin root originally meant "discerning" and is built from words meaning "between," "to choose," and "to read."