mer- / Indo-European roots
Examples of words with the root mer-: amaranth, ambrosia, amortize, amrita, Fomorian, immortal, manticore, marasmus, markhor, massicot, morbid, morbillivirus, mordacious, mordant, mordent, moribund, morsel, mort, mortal, mortar, mortgage, mortify, mortuary, murder, murrain, nightmare, postmortem, premorse, remorse.
To rub away, harm.
▲ Derivatives include nightmare, morsel, morbid, mortal, mortgage, ambrosia.
1. nightmare from Old English mare, mære, goblin, incubus, from Germanic *marōn-, goblin.
2. marasmus; amaranth from Greek marainein, to waste away, wither.
3. Perhaps suffixed o-grade form *mor-i- in Old Irish fomoire, fomoir, Fomorian, perhaps from earlier *wo-mor-i-, sinister supernatural being (*wo- under; < *upo-; see upo): Fomorian
4. Probably suffixed zero-grade form *mr̥-to-, "ground down" mortar from Latin mortārium, mortar.
5. Possibly extended root *merd-. mordacious, mordant, mordent, morsel; premorse, remorse from Latin mordēre, to bite.
6. Possibly suffixed form *mor-bho-. morbid from Latin morbus, disease (but this is more likely of unknown origin).
II. Possibly the same root is *mer-, "to die" with derivatives referring to death and to human beings as subject to death.
1. Zero-grade form *mr̥-. a. Suffixed form *mr̥-tro-. murder from Old English morthor, murder, from Germanic suffixed form *mur-thra-; b. suffixed form *mr̥-ti-. mort1, mortal; amortize, mortify, postmortem from Latin mors (stem mort-), death; c. suffixed form *mr̥-yo-. moribund, mortgage, mortmain, mortuary, murrain from Latin morī, to die, with irregular past participle mortuus (< *mr̥-two-), replacing older *mr̥-to- (for which see d); d. prefixed and suffixed form *n̥-mr̥-to-, "undying, immortal" *n̥-, negative prefix; see ne) (i) immortal from Latin immortālis; (ii) ambrosia from Greek ambrotos, immortal, divine(a- + -mbrotos, brotos, mortal); (iii) amrita from Sanskrit amṛtam, immortality (a- + mṛta-, dead)..
2. Suffixed o-grade form *mor-t-yo-. manticore from Greek mantikhōras (corrupted from marti(o)khōras), manticore, probably from Iranian compound *martiya-khvāra-, "man-eater" (*khvāra-, eating; see swel-) , from Old Persian martiya-, a mortal man.
[Pokorny 4. mer-, 5. mer- 735.]