Pill bug or wood louse (6)
I believe the answer is:
isopod
'pill bug or wood louse' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for isopod that I've seen before include "Woodlouse, say" , "This crusty creature" , "Slater, for instance" , "Crawler" , "Member of an order of crustaceans" .)