1.
cheap; inexpensive
Low in price. A somewhat old-fashioned usage.
2.
easy; simplistic; superficial
Taking the easy way without much thought or effort. Often carries a critical nuance of being too simple-minded or lazy in approach.
Sense 1 (cheap/inexpensive) is somewhat dated and rarely used in modern conversation. Sense 2 (easy/simplistic) is the more common modern usage and almost always carries a negative nuance — it criticizes a lack of serious thought or effort. Common collocations: 安直な考え (simplistic thinking), 安直に考える (to think too simply), 安直な方法 (an easy/lazy method).
Related Words
Compare:
短絡的 (hasty)