What is Agnati?

Legal Definition
In descents. Relations on the father's side: they are different from the cognati, they being relations on the mother's side, affines, who are allied by marriage, and the propinqui, or relations in general. 2 Bl. Com. 235; Toull. Dr. Civ. Fr. tome 1, p. 139; Poth. Pand. Tom. 22, p. 27. Calvini Lex.
-- Bouviers Law Dictionary
Legal Definition
In Roman law. The term included "all the cognates who trace their connection exclusively through males. A table of cognates is formed by taking each lineal ancestor in turn and including all his descendants of both sexes in the tabular view. If, then, in tracing the various branches of such a genealogical table or tree, we stop whenever we come to the name of a female, and pursue that particular branch or ramification no further, all who remain after the descendants of women have been excluded are agnates, and their connection together is agnatic relationship." Maine, Anc. Law, 142.

All persons are agnatically connected together who are under the same patria potestas or who have been under it or who might have been under it if their lineal ancestor had lived long enough to exercise his empire. Maine, Ana Law, 144. The agnate family consisted of all persons living at the same time, who would have been subject to the patria potestas of a common ancestor, if his life had been continued to their time. Hadl. Rom. Law, 131.

Between agnati and cognati there is this difference: that, under the name of agnati, cognati are included, but not C converso; for instance, a father's brother, that is, a paternal uncle, is bath agnatus and cognatus, but a mother's brother, that is, a maternal uncle, ls a cognatus but not agnatus. (Dig. 38, 7, 5, pr.) BurrilL
-- Black's Law Dictionary
Legal Definition
Romans who traced their name and lineage through the male line to a common deceased ancestor.
-- Ballentine's Law Dictionary