Severe German, on edge (4)
I believe the answer is:
grim
'severe' is the definition.
(thesaurus)
'german on edge' is the wordplay.
'german' becomes 'g' (abbreviation).
'on' says to put letters next to each other.
'edge' becomes 'rim' (rim is a kind of edge).
'g'+'rim'='GRIM'
(Other definitions for grim that I've seen before include "Serious, forbidding" , "The - Reaper is death" , "Forbidding harsh and unpleasant" , "(Of humour) black; unappealing, depressing" , "Very serious, gloomy" .)