1) Casual 2) Composed 3) Cool 4) Even 5) Even tempered 6) Sedate 7) Stoic 8) Unflappable 9) Unshaken 1) Composed 2) French word used in English 3) Keeping calm 4) Not easily excited 5) Unflappable 6) Unruffled 
Im`per·turb'a·ble adjective [ Latin imperturbabilis ; prefix im- not + perturbare to disturb: confer French imperturbable . See Perture .] Incapable of being disturbed or disconcerted; as, imperturbable gravity. 
calm not capable of being excited 
[adj] - not easily perturbed or excited or upset
imperturbable, imperturbably, imperturbableness 1. Not easily perturbed or excited or upset. 2. Marked by extreme calm and composure.
unflappable adjective not easily perturbed or excited or upset; marked by extreme calm and composure; `hitherto imperturbable, he now showed signs of alarm`; `an imperturbable self-possession`; `unflappable in a crisis`
incapable of being upset or agitated; not easily excited; calm: imperturbable composure.
marked by extreme calm and composure[Intelligent words] marked by extreme calm and composure