Possible Clues:

• Of __: helpful for
• ''To breathe such vows as lovers ___ swear'' (Shak.)
• Was of __: helped
• Be of __: help
• Be of ___ (help)
• Be of ___ (aid)
• Be of ___ (avail)
• Is of __ (helps)
• Be of __ (assist)
• Is of ___ (helps)