sag
v.
late 14c., possibly from a Scandinavian source related to Old Norse sokkva "to sink," or from Middle Low German sacken "to settle, sink" (as dregs in wine), from denasalized derivative of Proto-Germanic base *senkwanan "to sink" (see sink, v.). A general North Sea Germanic word (compare Dutch zakken, Swedish sacka, Danish sakke). Of body parts from 1560s; of clothes from 1590s. Related: Sagged; sagging.
n.
1580s, in nautical use, from sag, v.. From 1727 of landforms; 1861 of wires, cables, etc.
词根：sag = to perceive
来自拉丁语的sag意为to perceive。
同源词：
1. presage（事先感觉、感知pre(=before) +sag(=perceive)）
vt.预示；预言；预知，预感
n.前兆，预感；预知
Chest and arm pains,nausea,and shortness of breath can presage a heart attack.胸部和手臂疼痛、恶心以及气短都可能是心脏病发作的前兆。
2. sage
n.贤人，哲人 adj.智慧的；贤明的；<谑>道貌岸然的；一本正经的
3. sagacious
adj.精明的；有洞察力的；（动物）伶俐的
4. sagacity
n.贤明；睿智
Sagacity,unlike cleverness,may increase with age.与伶俐不同，睿智可能会随着年龄的增长而增长。
词根：sag = know, 表示“知道”
sage n. 贤人，哲人
sagacious a. 精明的，智慧的（sag+aclous多…的→知道很多的→智慧的）
presage n. 预感，预兆（pre预兆+sage→预先知道→预感）
sapience n. 智慧（sap[=sag]+ience表名词）