I am pretty sure like algol like languages FP isn't a monolith it is a broad stroke combination of the following things
functions, types and values are often on the same plane (like Lean, Coq, etc) or types and (functions + values) have a clear separation but one can create multiple hierarchies in those 2 levels (OCaml, Haskell, etc)
they often use immutable data structures or explicitly state if it is mutable
every line is a program is an expression, when it is a statement it still returns some signal (usually unit)
lispy langs or other gradually typed languages are not statically type checked and ML like langs are statically type checked
Also all these features are ime just how I want to do programming. It is merely a subjective thing which I find comfortable to program in.
Crosswords