first pine; closest pine to the Noh stage
Refers to the pine tree closest to the Noh stage among the three placed in front of the bridge walkway (hashigakari). A specialized term used in Noh theater context.
On the Noh stage, three pine trees are depicted in front of the bridge walkway, and the one closest to the stage is called the first pine (一の松).
Compound of 一 (ichi, 'one' or 'first') + の (no, possessive particle) + 松 (matsu, 'pine tree'). The term is specific to Noh theater staging conventions.