half-life

n time taken for the radioactivity of a substanceto fall to half its original value 半衰期（某物质的放射性元素由原有量衰减到一半所需的时间）.

half, half board, half cock, half holiday, half moon, half nelson, half pay, half-and-half, half-back, half-baked, half-brother, half-caste (also half-breed), half-crazed, half-crown, half-dozen, half-hardy, half-hearted, half-heartedly, half-hourly, half-length, half-light, half-listen, half-mast, half-naked, half-note, half-price, half-seas-over, half-sister, half-size, half-term, half-timbered, half-time, half-tone, half-track, half-truth, half-way, half-whisper, half-wit, half-witted, half-yearly,