Invest in many a broken-down hotel (6)
I believe the answer is:
clothe
'invest' is the definition.
('clothe' can be a synonym of 'invest')
'many a broken-down hotel' is the wordplay.
'many' becomes 'c' (C is the Roman numeral for 100).
'a broken down' indicates an anagram.
'hotel' is an anagram of 'lothe'.
'c'+'lothe'='CLOTHE'
'in' is the link.
(Other definitions for clothe that I've seen before include "robe" , "Equip" , "Put garments onto" , "Invest" , "apparel" .)