Nominal Relative Clauses: What, Whatever, Whoever, and Whichever

In I understand what you mean, the word what does the work of both “the thing” and a relative marker. That makes the clause nominal: the whole unit behaves like a noun phrase.

What is not the same as that which in everyday style

What I need is time means roughly the thing that I need is time. There is no separate antecedent before what. This distinguishes nominal relatives from the ordinary relative clauses covered in Who, Which, and That.

-ever forms add openness or indifference

• Whoever finishes first can leave. — any person who finishes first.
• Take whichever route is faster. — any route from the relevant set.
• Whatever she decides, we will support her. — her exact decision does not alter the main outcome.

Function matters more than the label

Nominal relatives can be subjects, objects or complements: What happened next surprised everyone. / I remember what he said. / This is exactly what we expected. If you are comfortable with noun clauses, compare how both clause types occupy noun-like positions while using different internal structures.

Diagnostic: if you can replace the whole clause with something, someone or the thing/person that…, you are probably looking at a nominal relative.