means Free from tension, anxiety, or strain — physically loose and mentally at ease.

from From Latin 'relaxare,' to loosen or open up, built from 're-' (back, again) and 'laxare' (to slacken), itself from 'laxus,' loose or slack — the same root that gives us 'lax.' It arrived in English through the 14th century, first describing things physically loosened or eased; the sense of a person being mentally unwound came later, as if the mind were a muscle that could finally let go its grip.