helpmate (n.)

also help-meet, a ghost word from the 1611 "King James" translation of the Bible, in which it was at first a two-word noun-adjective phrase translating Latin adjutorium simile sibi [Genesis ii.18] as "an help meet for him," and meaning literally "a helper like himself." 

Robert Alter ("The Five Books of Moses," 2004) suggests sustainer beside him as the closest possible in English to the original:

The Hebrew 'ezer kenegdo (King James Version "help meet") is notoriously difficult to translate. The second term means "alongside him," "opposite him," "a counterpart to him." "Help" is too weak because it suggests a mere auxiliary function, whereas 'ezer elsewhere connotes active intervention on behalf of someone, especially in military contexts, as often in Psalms. ["Five Books of Moses," footnote to Gen. ii.18].

See help (n.) + meet (adj.) "proper, appropriate," also "fit (to do something)." By 1670s it was hyphenated, help-meet, and mistaken for a modified noun. Compare helpmate.