Definition of primer seisin in English:

primer seisin

noun

Feudal Law
historical
  • The right of the English Crown, on the death of a tenant-in-chief, to take and retain seisin of land until the heir has performed homage and paid relief (subsequently regarded as equivalent to the profits of the inherited estate for the first year).

Origin

Late 15th century; earliest use found in Rolls of Parliament. After Law French primer seisin; compare post-classical Latin seisina prima.