Five in a dreadful hole - veritable slum (5)
I believe the answer is:
hovel
'veritable slum' is the definition.
'hovel' can be an answer for 'slum' (thesaurus). I'm not certain of the 'veritable' bit.
'five in a dreadful hole' is the wordplay.
'five' becomes 'V' (Roman numeral).
'in' means one lot of letters goes inside another.
'a dreadful' indicates an anagram.
'hole' anagrammed gives 'hoel'.
'v' inserted inside 'hoel' is 'HOVEL'.
Can you help me to learn more?
(Other definitions for hovel that I've seen before include "Dirty, neglected dwelling" , "Crude dwelling" , "Small crude shelter" , "Wretched building" , "Mean dwelling" .)