• hazardest,
• hearvest,
• hardist,
• haydent,
• hadent,
• harderd,
• hapiest,
• hardend,
• weardest,
• headest,
• hardess,
• harverst,
• hardes,
• handesd,
• hartiest,
• hradest,
• hadest,
• heardest,
• harders,
• harest

• hard disk,
• Hardison,
• hard sell,
• hardship,
• hardiest,
• hard disc,
• handiest,
• harvest,
• hardegree,
• headrest,
• hard tick,
• hardcastle,
• hades,
• hardtack,
• heartiest,
• hardesty,
• Hardisty,
• hard steel,
• hardcore,
• Hardge,
• hardage.

The adjective form of the word "hardest" is "hardest".

The plural form of the word "hardest" is "hardests"

The singular form of the word "hardest" is "hardest" as it is already in its superlative form.