Rocks and water guarding top-class freezer (8)

'freezer' is the definition.
(thesaurus)

'rocks and water guarding top-class' is the wordplay.
'rocks' becomes 'ice' (as in a drink on the rocks).
'and' says to put letters next to each other.
'water' becomes 'hose' (water a flowerbed say).
'guarding' means one lot of letters goes inside another.
'top-class' becomes 'U' (as in U and non-U speech).
'hose' going around 'u' is 'house'.
'ice'+'house'='ICEHOUSE'