> I understand this verb to refer to sentencing something to
> destruction, which for living things is a sentence of death.
> For something devoted to the Lord, to the giver it is the
> same as dead or destroyed in so far as he can no longer make
> use of it.
To the giver, yes. The priests can make use of it though, in some cases
(Num. 18:14; Ezk. 44:29)
> Is there connection between this and a (fish) trap?
If there is a relation it is an etymological one. The basic meaning of
X-R-M is "to split" (Lev. 21:8; Isa. 11:15). This word may have
developed in two directions:
(1) to split > to set apart for God
(2) to split > to separate (e.g. by leading into a fish trap?)
Synchronically though, we can simply conclude that the noun XEREM has
two meanings, whether etymologically related or not:
(1) fishing net, fish trap
(2) state of having been set apart