Fillip

n.

1. something which acts as a stimulus or boost to an activity. “the halving of the automobile tax would provide a fillip to sales”
2. ARCHAIC a movement made by bending the last joint of the finger against the thumb and suddenly releasing it; a flick of the finger. “the Prince, by a fillip, made some of the wine fly in Oglethorpe’s face”

v.

1. ARCHAIC fillip; 3rd person present: fillips; past tense: filliped; past participle: filliped; gerund or present participle: filliping propel (a small object) with a flick of the finger. “our aforesaid merchant filliped a nut sharply against his bullying giant”

[The 7 Deaths of Evelyn Hardcastle — Stuart Turton]