Sucker will disbelieve the basic truth, last of all (5)

I believe the answer is:

leech

'sucker' is the definition.
(thesaurus)

'will disbelieve the basic truth last of all' is the wordplay.
'last of all' says to take the final letters.
The final letters of 'will disbelieve the basic truth' are 'LEECH'.

(Other definitions for leech that I've seen before include "Bloodsucker; early doctor" , "sponge" , "Annelid worm, used in medicine of old" , "Blood-sucking parasite" , "Old medicinal sucker" .)

I've seen this clue in The Times.

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