Lewis & Short

pillĕus, i, m., and pillĕum, i, n. [akin to Gr. πῖλος, with same signif.; also to pilus, a hair], a felt cap or hat, made to fit close, and shaped like the half of an egg. It was worn by the Romans at entertainments and festivals, esp. at the Saturnalia, and was given to a slave at his enfranchisement as a sign of freedom (cf. petasus).

  1. I. Lit.: pilleum quem habuit deripuit, Plaut. Fragm. ap. Non. 220, 14; id. Amph. 1, 1, 305: haec mera libertas, hanc nobis pillea donant, id. Pers. 5, 82. Free-born persons who had fallen into captivity also wore the pilleus for a while after the recovery of their freedom, Liv. 30, 45; 34, 52; Val. Max. 5, 2, 5 and 6. Gladiators who had often been victorious also received the pilleus at their discharge, Tert. Spect. 21. There were also leathern pillei, called Pannonian, which were worn by soldiers when off duty, in order that, by being always accustomed to wear something on their heads, the helmet might seem less burdensome, Veg. Mil. 1, 20.
  2. II. Meton.
    1. A. Liberty, freedom: servos ad pilleum vocare, to summon the slaves to freedom, Liv. 24, 32; Suet. Tib. 4; Sen. Ep. 47, 16; Val. Max. 8, 6, 2: totis pillea sarcinis redemi, i. e. I have made myself independent by selling all my goods, Mart. 2, 68, 4.
    2. B. A protector: te obsecro, Pilleum meum, mi sodalis, mea salubritas, Plaut. Fragm. ap. Non. 220, 16.
    3. C. The membrane which envelops the head of the fœtus, a child’s caul, Lampr. Diadum. 4.