WordNet sense 1 (the absence of mental stress or anxiety):

peace, peacefulness, serenity, ataraxis, heartsease, peace of mind

WordNet sense 2 (a disposition free from stress or emotion):

placidity, quiet, tranquility, tranquillity

WordNet sense 3 (be inherent or innate in):

reside, rest, reside

WordNet sense 4 (lean in a comfortable resting position):

recline, recumb

WordNet sense 5 (put in a horizontal position):

lay, put down

WordNet sense 6 (freedom from activity (work or strain or responsibility)):

ease, relaxation