What does "unflappable" mean?

Remaining composed and level-headed at all times; impossible to fluster; not becoming frustrated or irritated easily.

What is a synonym for "unflappable"?

Common synonyms include: imperturbable, assured, balanced, bovine, calm, collected.

Pronounced //ʌnˈflæpəbəl//.

/ʌnˈflæpəbəl/ adj

adj ·Uncommon ·College level

Adjective

1
Remaining composed and level-headed at all times; impossible to fluster; not becoming frustrated or irritated easily.
"The whole thing looked remarkably like an implacable force meeting an unflappable object."

Adjective

1
not easily perturbed or excited or upset; marked by extreme calm and composure wordnet

"Tom's unflappable, even under great pressure."

From un- + flap (“to upset, stir”) + -able.