Possible Clues:

• Said "bos'n" or "cap'n," say
• Omitted from a speech?
• Dropped a phoneme
• Fifty-one shortened, indeed
• Neglected to say, maybe
• Shortened to fifty-one indeed
• Skipped a phoneme
• 'With cover in the river up there, it's been shortened, in a manner of speaking (6)'
• Said 'bos'n' for 'boatswain,' e.g.
• Ran together, in a manner of speaking