De cierto fuste

De cierto fuste
 

Does this mean : of a certain ilk/de un cierto índole?

Depende un poco del contexto. Puede significar "de cierta índole", pero también de "una categoría importante." :)

Right - "substance", "importance", also "of a certain fibre" as in quality,
caliber...

My grandmother said oftentimes: "¡Qué poco fuste tiene esta muchacha!" Meaning, that the girl was kind of frivolous, dealing with trifling matters...

The sense of "importance" seems to be prevalent in my book. Moliner gives,
fuste 6 Considerable importancia o categoría de una persona: ‘Hombre de fuste’. También se aplica a cosas: ‘Una empresa de fuste’.

Oxford Superlex gives,
fuste m
1 a (importancia): un individuo que no tiene fuste = an insignificant o inconsequential individual, an individual of no consequence; un político/escritor de fuste = a politician/ writer of some standing :)

agree with all.
As you see, "fuste" is the big "portion" of a column, or a tree. It's the visible height. It's the visible reason of the existence, the "fundamental"
RAE
So when somebody or something is "de poco fuste" you're literally implying it's a small tree, a little column, something you don't care or a variable person.
saying "de cierto fuste" you're saying the person/thing has some standing, or it's not variable.
saying "de mucho fuste" you're saying it's a big/important thing, or he's not easy to move from a certain position.
this later term is used ironically sometimes "allá va, creyéndose una persona de gran fuste/there he goes, thinking he's somebody important/a significant person"

saludos :D

saludos

¡Gracias, Sosia! Tus ejemplos han explicado mucho: la función de "cierto" esa expresión no era clara para mi antes.
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Thank you, Sosia. Your examples have explained a lot: the function of "cierto" was unclear to me previously.

you're welcome :D :D :D