Collier and Co have a ship that holds a thousand (4,5)
I believe the answer is:
coal miner
'collier' is the definition.
(synonyms)
'co have a ship that holds a thousand' is the wordplay.
'have' is a charade indicator (letters next to each other).
'ship' becomes 'liner' (as in an ocean liner).
'that holds' means one lot of letters goes inside another.
'a thousand' becomes 'M' (Roman numeral for a thousand).
'liner' going around 'm' is 'lminer'.
'co'+'a'+'lminer'='COAL-MINER'
'and' is the link.
(Other definitions for coal miner that I've seen before include "person working mostly in the dark" , "I'm dirty when I'm working" , "No miracle (anag) - endangered species?" , "Digger" .)