Mob boa wriggling in grass (6)
I believe the answer is:
bamboo
'grass' is the definition.
(thesaurus)
'mob boa wriggling' is the wordplay.
'wriggling' is an anagram indicator.
'mob'+'boa'='mobboa'
'mobboa' is an anagram of 'BAMBOO'.
'in' acts as a link.
(Other definitions for bamboo that I've seen before include "Thick tropical cane" , "Panda's staple diet" , "Treelike tropical grass" , "Giant tropical grass" , "'Tall, rigid grass (6)'" .)