Characterised by precipitation (5)
I believe the answer is:
rainy
'characterised by precipitation' is the definition.
I can't judge whether this defines the answer.
'characterised by precipitation' is the wordplay.
'characterised' becomes 'y' (I am not sure about this - if you are sure you should believe this answer much more).
'by' means one lot of letters go next to another.
'precipitation' becomes 'rain' (rain is a kind of precipitation).
'y' after 'rain' is 'RAINY'.
Can you help me to learn more?
(Other definitions for rainy that I've seen before include "Pluvial" , "With water falling outside" , "Drizzly" , "Wet, showery" , "(Of weather) wet" .)