One root, two faces that turn out to be one. The biblical sense is to inherit, and the inherited thing is the נַחֲלָה, the family estate. But the same letters name the נַחַל, the streambed that carves the land you inherit, and the act of settling on it. Inheritance, land, and the water that shapes it all braid into one idea: the portion that becomes yours. Every word here is verified against pealim, niqqud included.
The same root runs through the verb system. Each binyan is a voice: it bends the one idea into active, passive, causative or reciprocal. Tap to hear.
Pa'al לִנְחֹל is the original "receive a portion as your own" (today also "to win, to suffer" a defeat or victory). Hitpa'el לְהִתְנַחֵל turns that into the act of physically settling the land, and feeds the loaded modern noun הִתְנַחֲלוּת. The passive and causative binyanim are not lexicalized here; the root works through pa'al, hitpa'el, and its rich set of nouns.
Same root letters, different noun moulds (mishkalim). The mould tells you the function: who does it, the act of doing it, or the thing produced.
Strip the prefixes, suffixes and vowels. Three consonants remain, and the meaning lives there.