One in tank perhaps a printer when out of joint (8)
I believe the answer is:
terrapin
'out of joint' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'one in tank perhaps a printer' is the wordplay.
'a printer' anagrams to 'TERRAPIN'.
Though, I'm not clear how the anagram is indicated.
'when' is the link.
Can you help me to learn more?
(Other definitions for terrapin that I've seen before include "Aquatic tortoise" , "Give out" , "Hardback" , "Water tortoise" , "Chelonian reptile" .)