A rare, poetic term for a flower bud, used in classical or literary contexts. Cross-referenced with つぼみ, which is the common modern word.
See also: 蕾
In old waka poems, '花の下紐' can refer to a flower bud.
The term is a classical compound of 花 (flower) + の (possessive particle) + 下紐 (undersash, cord). The exact derivation is uncertain; it may be a metaphorical expression for a bud as something tied or wrapped beneath the flower.