"main" + "man-" + "man"

these two stems bring about much misunderstandings about their kinship, but let's have a look at their "wild lives":

"main" (in English)

the (most) "able"

• Old English mæġen ("strong", "main", "principal")
  • Proto-Germanic *maganą ("to be able")
    • PIE *megh- ("to be able")
    • cognate with Proto-Slavic *mogti / *mot'i ("to be able")
      • hence Russian мочь moch' ("to be able")

"main" (in French)

the "hand"

• Latin manus ("hand")
  • Proto-Italic *manus ("hand")
    • [perhaps] PIE *(s)meh₂- ("to beckon")
    • cognate with Proto-Germanic *mundo ("hand")

note that Spanish mundo ("world") has its own thing:

• Latin mundus ("pure")
  • [perhaps] Etruscan muth ("pit")
  • [perhaps] PIE *mh2nd- ("to adorn") or *m(y)ewh1 ("to wash")

"man-"

a root that comes from the manus word above, e.g.:

• manipulation
• manual
• manuscript

so words like those have nothing to do with "man" as in "man and wife" (!)

"man"

once had to do with any "human":

• Old English mann ("human being", "person", "man")
  • Proto-West Germanic *mann ("human being", "person", "man")
    • Proto-Germanic *mann- ("human being", "person", "man")
      • PIE *mon- ("man", "human being")
        • see Proto-Slavic mǫžь ("man", "husband")
        • then Russian муж muzh ("man", "husband")

"man" (in Icelandic)

the word for "man" as in the sense above is maður, but man in Icelandic also can mean "dare" or "remember":

• man as a "neuter" noun in Icelandic:
  • Icelandic mana ("to dare")
    • Proto-Germanic manōną ("to urge")
      • PIE *men- ("to think")
        • see mental + mind

• man as the "first- and third-person singular present indicative" of muna
  • Icelandic muna ("to remember")
    • Proto-Germanic munaną ("to remember")
      • akin to our memory
      • PIE *men- ("to think")

so the two senses likely came from the same PIE root as they both have to do with "thinking"

now all these "m-vowel-n" words seem to come from standalone beginnings, but even they seem to have something in common; let's look here:

• "to be able"
• "man"
• "think"

perhaps the (human) man was a "living being who could think" (they could "m*n") and that set off all those words we see today!