expression, godan verb (-ru)
poison someone; slip poison into someone's drink/food
Specifically refers to secretly administering poison, often by adding it to a drink or meal. The expression 一服盛る implies a single dose or act of poisoning.
彼は敵に一服盛ろうと企てた。
He plotted to poison his enemy.
誰かが彼の茶に一服盛ったらしい
It seems someone slipped poison into his tea.
expression, godan verb (-ru)
prepare a poison; make a poisonous dose
Refers to the act of preparing or mixing a poison, rather than the act of administering it. This sense is less common and often overlaps with the first sense in context.
毒草から一服盛る方法を教わった。
I was taught how to prepare a poison from poisonous herbs.