väsa

Swedish

väsa (present väser, preterite väste, supine väst, imperative väs)

to hiss (especially of a snake)
En orm ringlade fram till mig och väste
A snake slithered up to me and hissed
to wheeze
väsande andning
wheezing ("wheezing / hissing breathing")

An "ssss"-like hiss. For more "roar"-like hissing, like from an angry cat, see fräsa.
Sounds more sinister as opposed to angry compared to fräsa when used to describe a human voice.
Both fräsa and väsa appears to be common for angry swans, perhaps depending on if the sound is perceived as more cat-like or more snake-like.

Conjugation of väsa (weak)

	Active		Passive
Infinitive	väsa		väsas
Supine	väst		västs
Imperative	väs		—
Imper. plural¹	väsen		—
	Present	Past	Present	Past
Indicative	väser	väste	väss, väses	västes
Ind. plural¹	väsa	väste	väsas	västes
Subjunctive²	väse	väste	väses	västes
	Participles
Present participle	väsande
Past participle	—
¹ Archaic. ² Dated. See the appendix on Swedish verbs.