infrequent

a. 稀少的,珍贵的,罕见的

Explosions, though infrequent, are an occupational hazard for coal-miners.

矿井爆炸虽然不常发生, 但却是煤矿工人职业中的危险.

Difficult, incomplete, or infrequent evacuation of dry, hardened feces from the bowels.

便秘有困难的、不完全的或不经常从肠道排泄干燥且硬的大便