Old English mara "greater, more, stronger, mightier," used as a comparative of micel "great" (see mickle), from Proto-Germanic *maizon- (source also of Old Saxon mera, Old Norse meiri, Old Frisian mara, Middle Dutch mere, Old High German mero, German mehr), from PIE *meis- (source also of Avestan mazja "greater," Old Irish mor "great," Welsh mawr "great," Greek -moros "great," Oscan mais "more"), from root *me- (3) "big." Sometimes used as an adverb in Old English ("in addition"), but Old English generally used related ma "more" as adverb and noun. This became Middle English mo, but more in this sense began to predominate in later Middle English.
"Take some more tea," the March Hare said to Alice, very earnestly.
"I've had nothing yet," Alice replied in an offended tone, "so I can't take more."
"You mean you can't take less," said the Hatter: "it's very easy to take more than nothing."
More or less "in a greater or lesser degree" is from early 13c.; appended to a statement to indicate approximation, from 1580s.