1.slack的基本意思是指某人做某事时“懈怠,偷懒”,用于交通工具时指“减速”。
2.slack既可用作不及物动词,也可用作及物动词。用作及物动词时,接名词或代词作宾语; 用作不及物动词时,常与down, off, up等连用。

slack down(v.+adv.)
滞销 become unsalable
▲slack down
Retail business slacks down when employment drops.就业率低时零售业就不景气。

slack off(v.+adv.)
1.放松(绳索等) loosen (sth such as a rope)
▲slack sth⇔off
Slack off those ropes there, there's a storm coming!把那里的绳索放松,风暴就要来了!
2.松懈; 懈怠 become lazy or inactive
▲slack off
It's natural to slack off towards the end of a hard day's work.辛苦工作了一天,快结束时有所松弛是很自然的。
Haas slacked off in his work.哈斯工作很懈怠。
Don't slack off in your studies.不要荒废你的学业。
3.滞销 become unsalable
▲slack off
House sales in this city usually slack off during our severe winters.在严寒的冬季,这座城市的房产通常销路不好。
Business usually slacks off at this time of the year.每年这个时候生意一般都很清淡。

slack on(v.+prep.)
在…方面松散〔懈怠〕 become inactive on (sth)
▲slack on sth
The instructors were slacking on the job.教员们对工作松松垮垮。

slack up(v.+adv.)
(使)减速; (使)松劲 (cause to) reduce speed or effect
▲slack up
Slack up before you reach the crossroads.到交叉路口以前减速。
The doctor advised Facer to slack up for few days, as his lifestyle was having a bad effect on his heart.医生劝告费塞放松几天,因为他的生活方式对他的心脏产生了不良影响。
▲slack sth⇔up
Slack up the tent ropes before it rains.在下雨之前把帐篷的绳子放松。
Please slack up your speed,I can't run as fast as you!请你跑慢点!我跑得没你快。

用作不及物动词
▲S+～(+A)
Stop slacking and get on with digging.不要偷懒,继续挖。
His pace has gradually slacked.他的步速逐渐慢了下来。
The breeze slacked.风变小了。
用作及物动词
▲S+～+n./pron.
Slack the rope before trying to untie the knot.想解结之前先将绳索放松。

［同义词］ adj.  baggy, dull, easy, loose, quiet, slow
［反义词］ adj.  busy, diligent, quick, rigid, stiff
［词源］＜古英语slæc(松弛)

用作定语
▲～+n.
 He tightened a few slack screws.他旋紧了几只松动的螺丝。
Winter is the slack season at most hotels.对大多数旅馆来说,冬天是淡季。
用作表语
▲S+be+～
 Discipline in Mr. Brow's class becomes very slack.布朗先生班上的纪律很松。
Security's got a bit slack.安全问题有些放松。
▲S+be+～+prep.-phrase
 Living alone, he became slack about his appearance.由于单独过活,他对自己的外表越来越不在意了。
Don't get slack at your work.不要疏忽你的工作。
He is always slack in doing his homework.他做作业总是马马虎虎。
Nancy is slack in answering letters.南希很少回信。