noun
millet grain
Refers literally to a single grain of millet.
粟粒はとても小さい。
A millet grain is very small.
noun
something extremely tiny
Figurative use emphasizing extreme smallness, often in comparisons.
その傷は粟粒ほどだった。
The wound was as small as a millet grain.
Compound of 粟 (awa, 'millet') and 粒 (tsubu, 'grain'). The reading ぞくりゅう is the on'yomi reading, but it is rare and not commonly used.