| piarachnoid | The two delicate layers of the meninges, the arachnoid mater and pia mater (vs. The tough pachymeninx or dura mater), considered together; by this concept, the arachnoid and pia are two parts of a single layer, much like the parietal and visceral layers of a serous membrane or bursa; although separated by the subarachnoid space they are connected via the arachnoid trabeculae and become continuous where the nerves and filum terminale exit the subarachnoid space (the cerebrospinal fluid-filled space bounded by the leptomeninges). See: arachnoid, pia mater. Synonym: meninx tenuis, pia-arachnoid, piarachnoid. Origin: Lepto-+ G. Meninx, pl. Meninges, membrane (05 Mar 2000) |
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| piarist | One of a religious order who are the regular clerks of the Scuole Pie (religious schools), an institute of secondary education, founded at Rome in the last years of the 16th century. Origin: L. Pius pious. Source: Websters Dictionary (01 Mar 1998) |
| piassava | A fibrous product of two Brazilian palm trees (Attalea funifera and Leopoldinia Piassaba), used in making brooms, and for other purposes. Synonym: piacaba and piasaba. Origin: Pg. Piasaba. Source: Websters Dictionary (01 Mar 1998) |