Are these names trendy or timeless?
[name_f]Adeline[/name_f]
[name_f]Madeline[/name_f]
[name_f]Isabella[/name_f]
[name_f]Rosalie[/name_f]
I think all of these are timeless. I think the only one actually pushing more overused than trendy is [name_f]Isabella[/name_f].
All of them definitely lean towards timeless, [name_f]Rosalie[/name_f] especially. [name_f]Isabella[/name_f], [name_f]Adeline[/name_f], and [name_f]Madeline[/name_f] I think are going to feel a bit tied to a certain era ([name_f]Madeline[/name_f] - 1990s, [name_f]Isabella[/name_f] - early/mid 2000s, [name_f]Adeline[/name_f] 2010s) but in the same way [name_f]Mary[/name_f] is tied to the early 20th century, but it is still considered a classic name. Anecdotally, all of the Madelines/Maddies, Isabellas/Bellas, and Adelines/Addies I have met (and I have met or heard of many) are from the decades I noted, so I do feel, at least in the US, if you hear those names you can pretty easily guess when they were born.
Timeless, but [name_f]Rosalie[/name_f] and [name_f]Isabella[/name_f] were trendy in recent years due to Twilight.
[name_f]Adeline[/name_f] is the only one that feels somewhat trendy to me, although this is definitely the most classic spelling in use ([name_f]Adalynn[/name_f] etc are much more trendy to me). [name_f]Isabella[/name_f] and [name_f]Madeline[/name_f] are popular but not trendy to me, they might go down a little on the list in time but they will never completely fade out - similarly to 80s/90s names like [name_f]Lauren[/name_f] or [name_f]Sarah[/name_f], that feel tied to a certain time but were still given to thousands of babies last year, in comparison to [name_f]Crystal[/name_f], [name_u]Stacy[/name_u] and [name_f]Brandi[/name_f] that have all but disappeared at this point. And [name_f]Rosalie[/name_f] imo is not trendy or overly common at all!
All are trendy to me personally. [name_f]Isabella[/name_f] used to be my favorite name, but thanks to Twilight, EVERYONE had named their daughter [name_f]Isabella[/name_f], it seems 
I think all of these names will be strongly tied to women born in 2000-2020.
Currently, I would say that [name_f]Adeline[/name_f], [name_f]Isabella[/name_f] and [name_f]Rosalie[/name_f] sound classic but trendy- names that have been in use for centuries, but that are more popular right now than they have been for awhile. That is, the idea of an [name_f]Adeline[/name_f]/[name_f]Isabella[/name_f]/[name_f]Rosalie[/name_f] born in 1920 or 1950 or 1990 wouldn’t be completely bizarre the way a [name_u]Harper[/name_u] or [name_u]Wren[/name_u] born in those time periods would be, but on balance, it is likely that an [name_f]Adeline[/name_f]/[name_f]Isabella[/name_f]/[name_f]Rosalie[/name_f] would be under 10 years old right now.
[name_f]Adeline[/name_f] was [name_f]Virginia[/name_f] [name_m]Woolf[/name_m]'s first name, there was an [name_f]Isabella[/name_f] in at least two [name_f]Jane[/name_f] [name_u]Austen[/name_u] novels and there’s a [name_f]Rosalie[/name_f] in an [name_f]Anne[/name_f] [name_f]Bronte[/name_f] novel, so they’re certainly not modern inventions/coinages!
I would have said that [name_f]Madeline[/name_f] sounds a lot more trendy than the others, at least in English (I would have imagined much more of a history of use in [name_m]French[/name_m], or the [name_f]Madeleine[/name_f] spelling at least), but checking the stats it’s barely been out of the US top 500 since the list started in 1880, and in the top 200 for most of that time, so more classic than I’ve thought!
The other thing to remember is, it’s hard to tell which names will remain popular and eventually become classic. There were probably parents in the 1980s wondering if [name_f]Emma[/name_f] was too trendy, and it’s only become more popular since then; at this rate it will become the kind of classic like [name_f]Elizabeth[/name_f] that isn’t tied to any age group at all. An [name_f]Emma[/name_f] today could just as likely be a baby as a 30 year old- this may be [name_f]Adeline[/name_f]/[name_f]Isabella[/name_f]/[name_f]Madeline[/name_f]/[name_f]Rosalie[/name_f] in a few decades, or not, but it’s hard to predict trends decades in advance.
I agree with this, which makes them either ‘trendy’ or ‘on trend’ which seem to me to mean the same thing except one is a negative term - trendy, and the other more positive - on trend. [name_m]How[/name_m] one talks about currently popular names seems to have a lot to do with whether you like them or not.
I think they’re all timeless!