“The slackness in his driving was evident, as he weaved in and out of traffic without signaling.”
“The slackness of the rope was evident as it drooped limply from the tree branch.”
“Any slackness on Sunday against Tyrone and we'll be punished severely for it.”
slacks
(dated) (plural only) Semi-formal trousers that are less formal than those part of a suit but suitable for wearing in most offices and therefore nowadays no longer considered casual trousers. (Takes a plural verb even when referring to a single pair; may be referred to as a pair of slacks)