Related Clues:

• See 35-Across
• Closing envelopes
• Kind of wax
• Shutting up
• Purpose of some wax
• Making sound with sound of 17 across
• Securing ocean fish
• Making air/watertight
• Securely closing
• Giving authorisation to small London borough
• Making leakproof?
• By the sound of it, roof closing
• Waterproofing, say