Iambic ichor is an alembant that wits (but not fulgars) must take daily. It is the second most important alembant that wits must imbibe after Cathar's Treacle. Threnody's schedule involved her taking her daily dose of iambic ichor in the mornings.
An iamb is a metrical foot used in various types of poetry. Ichor is any fluid with the colour and consistency of blood and typically refers to monster blood, although it can also mean a discharge of pus.