@idefix37 A common expression for swell in italian is "onde di mare morto". See the picture attached taken from the book MANUALE DI INGEGNERIA PORTUALE E COSTIERA by Ugo Tomasicchio, https://www.hoepli.it/libro/manuale-di-ingegneria-portuale-e-costiera/9788820346430.html.
"mare morto" in italian means "dead sea" and I can't conceive waves as something dead. I personally do not like it and would prefer "mare di fondo". Since there may be more than one swell coexisting at the same time, we can name them in italian "mare di fondo 1", "mare di fondo 2", etc...
Summing up:

1. translating "swell" with "moto ondoso" is misleading
2. Swell in italian can be translated with "onde di mare morto"
3. I personally prefer the translation "mare di fondo", consistent with the spanish language
4. If in doubt, better to keep the expression "swell" in the italian version of windy.
   

@idefix37 A common expression for swell in italian is "onde di mare morto". See the picture attached taken from the book MANUALE DI INGEGNERIA PORTUALE E COSTIERA by Ugo Tomasicchio, https://www.hoepli.it/libro/manuale-di-ingegneria-portuale-e-costiera/9788820346430.html.
"mare morto" in italian means "dead sea" and I can't conceive waves as something dead. I personally do not like it and would prefer "mare di fondo". Since there may be more than one swell coexisting at the same time, we can name them in italian "mare di fondo 1", "mare di fondo 2", etc...
Summing up:

1. translating "swell" with "moto ondoso" is misleading
2. Swell in italian can be translated with "onde di mare morto"
3. I personally prefer the translation "mare di fondo", consistent with the spanish language
4. If in doubt, better to keep the expression "swell" in the italian version of windy.
   

@aruju

@idefix37 I guess the words "swell" and "ground swell" are synonyms. I agree that keeping the word "swell" as it is may be a good option especially if the translation in a particular language is a bit uncertain.

@Ondřej-Šutera In Spain (where I studied) there is a net distinction between wind waves ("mar de viento") and swell waves ("mar de fondo"). Attached is a snapshot taken from the Puertos del Estado (spanish government) webpage: https://www.puertos.es/es-es/Paginas/FAQ.aspx#faq13.
In italian the issue is a bit more open and ill-defined. Sometimes the words "mare lungo" or "mare morto" are used. The direct translations would be, respectively, "long sea" and "dead sea". Neither of them defines swell waves as they effectively are since they do not explain well the process of swell waves. Swell waves are those wave packets that are not forced by wind, but they are not necessarily long. Swell waves are usually identified from the wave spectrum as those wave components that have a celerity larger than the wind speed along the wave direction (including a factor as multiplier). I think that a reasonable solution would be to do as in the spanish language: wind waves are "mare di vento" and swell waves are "mare di fondo". In my opinion this is the word that better describes the phenomenon of swell waves in the italian language (moreover it is consistent with the spanish language which is similar to italian in many aspects). If you are not sure about the word "mare di fondo", just keep the english word "swell". The translation as it is now can be misleading. Cheers!!

Hi, the word swell cannot be translated as "moto ondoso" in italian. You can use "mare di fondo" instead, as "fondo" in italian means ground and swell in english comes from groundswell.