Solution

TOUGHEN

2 clues

Harden

Word class: Verb
Nature of clue: Synonym
Difficulty: Very easy
Sources: Boatload Puzzles

Other solutions to Harden

Strengthen

Word class: Verb
Nature of clue: Synonym
Difficulty: Very easy
Sources: Boatload Puzzles

Other solutions to Strengthen

Words are categorized by artificial intelligence: there can be mistakes.