In Tacitus: Annals: Book 2.71, Germanicus writes of his poisoning by what many (and I thought himself included) suspected was caused by Piso.
Yet in this paragraph Germanicus writes: "If any were touched by my bright prospects, by ties of blood, or even by envy towards me while I lived, they will weep that the once prosperous survivor of so many wars has perished by a woman's treachery."
So without further context this confuses me. Is he saying that Plancina, Piso's wife, was the mastermind behind the poisoning? Are there other women who may be suspected of having a hand in the poisoning? The only other explanation would be that "woman" is used derogatorily, but I've never seen it used in such a manner before.
The Latin says "muliebri fraude," "by womanly deceit." "Trickery" is a perfectly good translation of fraude, but unfortunately while "a woman's trickery" sounds much more natural in English and gets the point across, it's not what the Latin literally says. The Latin isn't necessarily condemning Plancina for the murder (although Germanicus has dragged her into his general spiel--"scelere Pisonis et Plancinae "--so Tacitus at least has Germanicus believing that she was in on it) but is condemning the deed as effeminate. "Muliebris" means womanly, or feminine, and almost always has a negative connotation, unless applied to, well, a woman. When a deed or a man is called womanly in Latin it's not a good thing. Poison is traditionally a very effeminate and cowardly method of murder and suicide in Latin literature--it's fitting, for example, that Plutarch has Cleopatra commit suicide by poison, since he paints her as this wacky eastern queen. Agrippina was accused of poisoning Claudius, Livia was accused of poisoning everybody in sight--especially for Tacitus poison is something that women resort to when they want to kill you. So both are possible here--Tacitus may be indicating that Germanicus thought that Plancina was in on it (as she might well have been, given what Tacitus says about her), and whether or not that's what he's doing he's certainly indicating that Germanicus' death by poison is a womanly and cowardly way to kill him, not at all fitting for him
Woman was used as an insult: you can find more information in almost any source on Roman sexuality, such as Judith Hallett's book 'Roman Sexualities'.
Essentially for a man to be womanly as opposed to masculine suggested that one, rather than being of an aggressive, conquering character, was passive and weak.