A free word, but it's dry (4)
I believe the answer is:
arid
'it's dry' is the definition.
(similar in meaning)
'a free' is the wordplay.
'free' becomes 'rid' (to be free of something is to be rid of it).
'a'+'rid'='ARID'
'word but' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for arid that I've seen before include "Parched, waterless" , "Dry and infertile" , "Dry, devoid of interest" , "(Of an area) very dry" , "Very dry; uninteresting" .)