Head off arm-in-arm showing tattoos (5)
I believe the answer is:
inked
'head off' is the definition.
The answer and definition are not the same part of speech. However, past participle verbs and adjectives can sometimes mean the same thing.
'arm-in-arm showing tattoos' is the wordplay.
I cannot really understand how this works, but
'in' is present in the answer.
The remaining letters 'ked' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for inked that I've seen is " black mark perhaps".)