Free end of string instrument lifted (6)
I believe the answer is:
gratis
'free' is the definition.
(synonyms)
'end of string instrument lifted' is the wordplay.
'end of' suggests the final letters.
'instrument' becomes 'sitar' (sitar is a type of musical instrument).
'lifted' shows that the letters should be reversed in order (going up in down clue).
The final letter of 'string' is 'g'.
'sitar' in reverse letter order is 'ratis'.
'g'+'ratis'='GRATIS'
(Other definitions for gratis that I've seen before include "On the house" , "Without payment" , "Free of charge" , "Free (Latin)" , "Free, at no cost" .)