This geminate root (the ר repeats) holds a single taste that becomes a feeling: bitter. As a bare adjective it is the taste on the tongue; soften it and it is only slightly bitter; lift it into Passover and it is maror, the bitter herb that makes the memory of slavery taste real. As a verb it turns transitive: to embitter, to make a life bitter. Each 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.
A small geminate family that lives mostly in adjectives. The pi'el לְמָרֵר is the everyday verb "to embitter"; the hif'il לְהָמֵר is archaic and mostly literary. There is no lexicalized pa'al, pu'al, huf'al or hitpa'el here. That is normal for a root whose centre of gravity is a quality, not an action.
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.