Thanks to German label (3)
I believe the answer is:
tag
'label' is the definition.
(I know that tag is a type of label)
'thanks to german' is the wordplay.
'thanks' becomes 'ta' (UK informal version of 'thank you').
'to german' becomes 'g' (abbreviation).
'ta'+'g'='TAG'
(Other definitions for tag that I've seen before include "Tie-on label" , "Label or sticker" , "stock quotation" , "Earmark" , "Identity disc" .)