lapse
noun
1 a momentary lapse of concentration:
failure, failing, slip, error, mistake, blunder, fault, omission, oversight, negligence, dereliction;
informal slip-up, fail.
verb
1 he let his membership lapse:
expire, become void, become invalid, run out, terminate, become obsolete.
2 do not let friendships lapse:
end, cease, come to an end, stop, terminate, vanish, disappear, pass, fade, fall away, dwindle, wilt, wither, die.