Possible Clues:

• Resolute; diamond (arch.)
• Hard worker having to accept a far from reasonable rise
• First man gets firm over the insect
• Obdurate and unyielding
• Stubbornly firm
• Worker behind a barrier that's not yielding
• A poet, unable to finish, holding a metre to be intractable
• One may be definite that this was the first of all the insects
• Firmly unchanging
• Resolute drivers not disheartened about barrier