Mettle

n.resilient, capablewarm

What it means

Courage, resolve, and strength of character revealed by difficulty.

Reach for it when praising how someone meets a real test rather than predicting untested toughness

The final steep ascent tested the young hikers' mettle.

everyday
backbone
when moral firmness resists social pressure
not when Backbone can shame people by implying weakness and sounds blunt.
everyday
grit
when sustained effort through difficulty deserves concise praise
not when Grit can romanticize needless hardship and ignore support or strategy.
warm
courage
when action proceeds despite fear
not when Courage can appear in one moment, while mettle often emerges across a test.
warm
inner strength
when personal resilience should be expressed gently
not when Inner strength is nonspecific and can imply hardship belongs to the individual alone.
warm
spirit
when morale and lively inner strength are central
not when Spirit can name mood or liveliness before character has been tested.
professional
resolve
when firm decision keeps effort directed
not when Resolve can be stubborn or misguided and does not prove character.
professional
tenacity
when persistent grip on a difficult goal matters
not when Tenacity can continue after evidence says the goal should change.
formal
fortitude
when enduring prolonged hardship with strength matters
not when Fortitude emphasizes endurance more than initiative or competitive spirit.
literary
stoutheartedness
when brave resolve suits an intentionally old-fashioned tone
not when The rare word is too ornate for direct modern praise.

test one's mettle
Leading the rescue would test her mettle and her judgment.
prove his mettle
He proved his mettle by correcting the failure before defending his decision.
show real mettle
The apprentice showed real mettle during the difficult second attempt.

The definition and the example on this page are written here. The dictionaries above ground which meaning is being described, not the wording.