häftig

See also: -haftig

Swedish

häftig (comparative häftigare, superlative häftigast)

(sudden and) forceful or intense (like a violent or intense release of energy); violent, intense, fierce, etc.
en häftig kemisk reaktion
a violent chemical reaction

en häftig armrörelse
a sudden, forceful arm movement

en häftig strid utbröt
a fierce battle broke out

en häftig brand
an intense fire

en häftig debatt
a fierce debate

häftig gråt
intense crying, wailing, etc.

häftig sjögång
heavy seas
- 1861, Hagberg, translation of Shakespeare's Othello, II, 1. Iago speaking
  Han är häftig och har ett mycket oregerligt sinne; det kan nog hända, att han slår efter dig
  Sir, he is rash and very sudden in choler, and haply may strike at you
easily angered (of a person or their temperament); volatile, hot-tempered, etc.
hans häftiga humör
his volatile temper
(colloquial) cool
en häftig sportbil
a cool sports car

en häftig upplevelse
a cool experience

en häftig film
a cool movie

(sense 3) now dominates in the sense that häftig will be understood as cool as long as something might reasonably be described as cool, rather than as one of the other senses.
Often has a slightly more intense feel in (sense 3) compared to cool (which also appears in Swedish), though it's subtle. Bungee jumping is more likely to be described as a "häftig upplevelse (“experience”)" than a "cool upplevelse," for example.

Inflection of häftig
Indefinite	Positive	Comparative	Superlative²
Common singular	häftig	häftigare	häftigast
Neuter singular	häftigt	häftigare	häftigast
Plural	häftiga	häftigare	häftigast
Masculine plural³	häftige	häftigare	häftigast
Definite	Positive	Comparative	Superlative
Masculine singular¹	häftige	häftigare	häftigaste
All	häftiga	häftigare	häftigaste
1) Only used, optionally, to refer to things whose natural gender is masculine. 2) The indefinite superlative forms are only used in the predicative. 3) Dated or archaic