pia ma·ter 
(mātər, mätər)
(mātər, mätər)n.
The fine vascular membrane that closely envelops the brain and spinal cord under the arachnoid and the dura mater.
[Middle English, from Medieval Latin pia māter : Latin pia, tender + Latin māter, mother (translation of Arabic 'umm raqīqa : 'umm, mother + raqīqa, tender).]
- Down syndrome
- down the drain
- down the hatch
- down the line
- down the road
- down the tube
- down the tubes
- down the tubes/tube
- down the wind
- downtick
- downtime
- down-to-earth
- down to the wire
- downtown
- downtrend
- downtrodden
- downturn
- down under
- downward
- downwardly
- downwash
- downwind
- down with
- downy
- downy brome