experiencing or accompanied by sleeplessness; "insomniac old people"; "insomniac nights"; "lay sleepless all night"; "twenty watchful, weary, tedious nights"- Shakespeare
showing sustained enthusiastic action with unflagging vitality; "an indefatigable advocate of equal rights"; "a tireless worker"; "unflagging pursuit of excellence"
not capable of being conquered or vanquished or overcome; "a tribute to his courage...and his unconquerable will"- R.E.Danielson; "faced unconquerable difficulties"
moving quickly and lightly; "sleek and agile as a gymnast"; "as nimble as a deer"; "nimble fingers"; "quick of foot"; "the old dog was so spry it was halfway up the stairs before we could stop it"
possessing or exerting or displaying energy; "an energetic fund raiser for the college"; "an energetic group of hikers"; "it caused an energetic chemical reaction"
extremely hot; "the fervent heat...merely communicated a genial warmth to their half-torpid systems"- Nathaniel Hawthorne; "set out...when the fervid heat subsides"- Frances Trollope
stubbornly unyielding; "dogged persistence"; "dour determination"; "the most vocal and pertinacious of all the critics"; "a mind not gifted to discover truth but tenacious to hold it"- T.S.Eliot; "men tenacious of opinion"