Anything that tends to arouse:
— His approval was an added fillip.

synonym: bonus.

Roget 615: motive, springs of action, wellsprings of action.    reason, ground, call, principle; by end, by purpose; mainspring, primum mobile [Lat.], keystone; the why and the wherefore; pro and con, reason why; secret motive, arriere pensee [Fr.]; intention etc. 620.    inducement, consideration; attraction; loadstone; magnet, magnetism, magnetic force; allectation^†, allective^†; temptation, enticement, agacerie^†, allurement, witchery; bewitchment, bewitchery; charm; spell etc. 993; fascination, blandishment, cajolery; seduction, seducement; honeyed words, voice of the tempter, song of the Sirens forbidden fruit, golden apple.    persuasibility^†, persuasibleness^†; attractability^†; impressibility, susceptibility; softness; persuasiveness, attractiveness; tantalization^†.    influence, prompting, dictate, instance; impulse, impulsion; incitement, incitation; press, instigation; provocation etc. (excitation of feeling) 824; inspiration; persuasion, suasion; encouragement, advocacy; exhortation; advice etc. 695; solicitation etc. (request) 765; lobbyism; pull [Slang].    incentive, stimulus, spur, fillip, whip, goad, ankus^†, rowel, provocative, whet, dram.    bribe, lure; decoy, decoy duck; bait, trail of a red herring; bribery and corruption; sop, sop for Cerberus.    prompter, tempter; seducer, seductor^†; instigator, firebrand, incendiary; Siren, Circe; agent provocateur; lobbyist.    ... show more

Roget 276: impulse, impulsion, impetus; momentum; push, pulsion^†, thrust, shove, jog, jolt, brunt, booming, boost [U.S.], throw; explosion etc. (violence) 173; propulsion etc. 284.    percussion, concussion, collision, occursion^†, clash, encounter, cannon, carambole^†, appulse^†, shock, crash, bump; impact; elan; charge etc. (attack) 716; beating etc. (punishment) 972.    blow, dint, stroke, knock, tap, rap, slap, smack, pat, dab; fillip; slam, bang; hit, whack, thwack; cuff etc. 972; squash, dowse, swap, whap^†, punch, thump, pelt, kick, punce^†, calcitration^†; ruade^†; arietation^†; cut, thrust, lunge, yerk^†; carom, carrom^†, clip [Slang], jab, plug [Slang], sidewinder [U.S.], sidewipe^†, sideswipe [U.S.].    hammer, sledge hammer, mall, maul, mallet, flail; ram, rammer^†; battering ram, monkey, pile-driving engine, punch, bat; cant hook; cudgel etc. (weapon) 727; ax etc. (sharp) 253.    [Science of mechanical forces] dynamics; seismometer, accelerometer, earthquake detector.    ... show more

Dutch: prikkel, vingerknip, knip
Polish: bonus