Possible Clues:

• See 18
• Substance or material - not spirit
• The trouble is that it's 6 down
• That's a septic sort of a business
• Such amount of horn, that's the trouble
• The trouble is that it's so yellow
• Has business got infected with this?
• Be of significance
• and 4 across, perhaps golf, for instance, may be taken as something quite natural
• That business of the horn on the Alps