Śatapatha Brāhmaṇa ("of a hundred paths") 13.6.2.1

13.6.2.1

atha yasmātpuruṣamedho nāma ime vai lokāḥ pūrayameva puruṣo yo'yam pavate so'syām puri śete tasmātpuruṣastasya yadeṣu lokeṣvannaṃ tadasyānnam medhastadyadasyaitadannam medhastasmātpuruṣamedho'tho yadasminmedhyānpuruṣānālabhate tasmādveva puruṣamedhaḥ

And as to why it is called Purushamedha:--The stronghold (pur) doubtless is these worlds, and the Purusha (spirit) is he that blows here (the wind), he bides (sî) in this stronghold (pur): hence he is the Purusha. And whatever food there is in these worlds that is its 'medha,' its food; and inasmuch as this is its 'medha,' its food, therefore (it is called) Purushamedha. And inasmuch as at this (sacrifice) he seizes men (purusha) meet for sacrifice (medhya), therefore also it is called Purushamedha.