Related Clues:

• He, say, last to move pieces in check
• Xenon or zirconium
• Constituent — habitat
• Iron perhaps used for cores to help cements?
• Oxygen, for example, just a hint?
• Al may represent one
• Say silver piece
• He, e.g
• Water, perhaps -- a small amount
• Source of heat for situation in which you're most effective
• Possibly copper’s sphere of operation
• Factor in - English workers in accommodation
• Natural environment for silver, say
• He perhaps needs part for water heater
• Terbium or erbium, e.g