Conceal a hundred and more (5)
I believe the answer is:
cover
'conceal' is the definition.
(covering is a kind of concealing)
'a hundred and more' is the wordplay.
'a hundred' becomes 'c' (Roman numeral).
'and' says to put letters next to each other.
'more' becomes 'over' (I've seen this before).
'c'+'over'='COVER'
(Other definitions for cover that I've seen before include "Totally obscure" , "Extend over (an area)" , "Mask, hide" , "Fielder" , "Encompass" .)