Possessio fratris
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
The possession or seisin of a brother; that is, such possession of an estate by a brother as would entitle his sister of the whole blood to succeed him as heir, to the exclusion of a half-brother. Hence, derivatively, that doctrine of the older English law of descent which shut out the halfblood from the succession to estates; a doctrine which was abolished by the descent act, 3 & 4 Wm. IV. c.
106 See 1 Steph. Comm. 385; Broom, Max. 532.