Crazy and motiveless! (4)

I believe the answer is:

loco

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This clue might be a double definition.

'crazy' is the first definition.
(loco can informally mean mad)

'motiveless' is the second definition.
Both the answer and definition are adjectives. Perhaps you can see a link between them that I can't see?

'and' acts as a link.

Can you help me to learn more?

(Other definitions for loco that I've seen before include "Railway engine - mad!" , "Slangily crazy" , "Barmy (Spanish) - engine (abbr)" , "Mad - train" , "In ... parentis, in place of parents" .)

I've seen this clue in the Evening Standard.

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