Old English bærlice "openly, clear, public;" see bare (adj.) + -ly (2). Meaning "only just, no more than," is recorded from late 15c. In Middle English it also could mean "solely, exclusively."
we were so far back in the theater, we could barely read the subtitles
she barely seemed to notice him
it was barely 5 a.m.
the network has barely 5 percent of viewers