Bit of glass lodged in bare butt (5)
I believe the answer is:
nudge
'butt' is the definition.
(thesaurus)
'bit of glass lodged in bare' is the wordplay.
'bit of' says to take the initial letters.
'lodged in' indicates putting letters inside.
'bare' becomes 'nude' (synonyms).
The initial letter of 'glass' is 'g'.
'g' going inside 'nude' is 'NUDGE'.
(Other definitions for nudge that I've seen before include "Gentle poke with elbow" , "Facility of pinball machine" , "Elbow someone gently" , "A gentle reminder?" , "Prod gently with elbow" .)