Mental weariness leads suit astray (9)

I believe the answer is:

lassitude

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'mental weariness' is the definition.
'lassitude' can be an answer for 'weariness' (I've seen this before). I am not sure about the 'mental' bit.

'leads suit astray' is the wordplay.
'astray' indicates an anagram.
'leads'+'suit'='leadssuit'
'leadssuit' with letters rearranged gives 'LASSITUDE'.

Can you help me to learn more?

(Other definitions for lassitude that I've seen before include "Sluggishness" , "30 [LETHARGY]" , "Listlessness, lethargy" , "Listlessness, fatigue" , "Is saluted with tiredness" .)

I've seen this clue in The Independent.

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