Look back on motorway with a glower (8)
I believe the answer is:
remember
'look back' is the definition.
(thesaurus)
'on motorway with a glower' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'motorway' becomes 'M' (as in motorway names - M1, M4 etc).
'with' means one lot of letters go next to another.
'a glower' becomes 'ember' (something which glows).
're'+'m'+'ember'='REMEMBER'
(Other definitions for remember that I've seen before include "Keep in mind" , "Recall from memory" , "Commemorate" , "Retain memory of" , "Summon back to mind" .)