infrequence
n. 很少发生;罕见(等于 infrequency)
例句
The doctors were overwhelmed by the infrequence of the illness, however they calmed down at once and they began to examine my husband.
病情的罕见,把医生们都吓倒了,但是他们很快冷静下来,给病人做全身检查。