1650s, "powerful in operation," from Greek energetikos "active," from energein "to work, be in action, act upon" (see energy). Of persons, "active," in English from 1796 (energetical "operative" is from c. 1600; from 1630s as "full of energy," while energical is attested from 1560s). Related: Energetically.

"energetic force; motive force," 1894, from dynamic (adj.). As "manner of interaction," by 1978.

1927, originally hobo slang, "counterfeit seizures induced to attract sympathy;" meaning "energetic celebration" is by 1949. As a type of dingbat fonts made by Microsoft, from 1990.

1570s, "cause to become slower;" 1610s, intransitive, "become lax, remiss, or less energetic;" from slack (adj.) + -en (1). Formed after the sense specialization of slake (v.). Related: Slackened; slackening.

c. 1600, of insects, agent noun from hum (v.). Meaning "energetic person or thing" is 1680s; that of "excellent person or thing" is slang from 1907. As short for Humvee, attested from 1983.

"lively, energetic," 1590s, from spirit (v.) in its older sense. Milton uses it to mean "possessed by a spirit." Related: Spiritedly; spiritedness.

1920 in the political sense of "advocating energetic action;" see active + -ism. Earlier (1907) it was used in reference to a philosophical theory. Compare activist.

1590s, "to make more active or energetic" (of blood, alcohol, etc.), from spirit (n.). The meaning "carry off or away secretly" (as though by supernatural agency) is first recorded 1660s. Related: Spirited; spiriting.

1825, "thief" (especially one who roughs up his victims), from hustle (v.) + -er (1). Sense of "one who is energetic in work or business" (especially, but not originally, a salesman) is from 1884; sense of "prostitute" dates from 1924.

Old English liflic "living, existing," literally "life-like;" from life + -ly (2). The main modern sense of "active, energetic" developed by early 13c., from notion "full of life." For "full of life, vigorous," Old English had liffæst. The adverb is Old English liflice "vitally," from the adjective. Related: Liveliness.