main: [OE] Main goes back to prehistoric Germanic *mag- ‘be able, have power’ (source also of English may and might, and distantly related to machine). From it was descended Old English mægen ‘strength’. This now survives as a noun only in the expression with might and main, but it was also used attributively in Old English to mean ‘of large size, great’, and by the 13th century (helped along partly by the related Old Norse megenn or megn ‘strong’) it was being used as an adjective in its own right. At first it still meant just ‘large’, but by the 15th century its modern sense ‘chief’ had evolved. => may, might
