At its core this root means to keep, to keep watch over. The old pa'al נָטַר guards a vineyard, and by a famous twist also "keeps" a grudge: to bear a grudge is, in Hebrew, to guard resentment, never letting it go. Modern Hebrew put the root to fresh work in the pi'el לְנַטֵּר, to monitor, and its noun נִטּוּר, the monitoring that runs in hospitals, networks, and labs. The cousin מַטָּרָה (target) sits nearby: the thing you keep your eyes fixed on. 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.
The pa'al is the old, literal guard (and its idiom "to keep a grudge"). The pi'el is the modern technical verb, to monitor, which is why its action-noun נִטּוּר is everywhere in medicine and computing. Nif'al, hif'il and the passives are not lexicalized for this root.
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.