Understanding German file (5)
I believe the answer is:
grasp
'understanding' is the definition.
(grasp is a kind of understanding)
'german file' is the wordplay.
'german' becomes 'g' (abbreviation).
'file' becomes 'rasp' (rasp is a kind of file).
'g'+'rasp'='GRASP'
(Other definitions for grasp that I've seen before include "Support; rugby player" , "Seize - comprehend" , "Comprehension" , "Seize firmly - or understand (5)" , "Keep tight hold" .)