From Latin 'fīlius' (son), from PIE *dʰeh₁(y)- (to suckle) — defining the child-to-parent bond, as in 'filial piety.'
Of, relating to, or due from a son or daughter; denoting the relationship of offspring to parents.
From Late Latin 'filialis' (of a son or daughter), from Latin 'filius' (son) and 'filia' (daughter), from PIE *dheh₁(y)- (to suckle, nurse), reflecting the ancient definition of a child as 'one who is nursed.' This root connects 'filial' to an unexpectedly rich semantic network: Latin 'femina' (woman, literally 'she who suckles'), yielding 'feminine,' 'female,' and 'effeminate'; Latin 'felix' (fruitful, happy, fortunate — originally 'fertile'), giving 'felicity' and 'felicitous'; Latin 'fecundus' (fruitful), giving 'fecund'; and Greek 'thele' (nipple), giving 'epithelium' (the tissue 'upon the nipple'). The word entered English in the 15th century through
In genetics, 'F1' and 'F2' stand for 'first filial generation' and 'second filial generation' — the offspring of a cross and their offspring in turn. Gregor Mendel's pea plant experiments, the foundation of modern genetics, are described entirely in terms of filial generations.