lower (v.1)youdaoicibaDictYouDict[lower 词源字典]
c. 1600, "to descend, sink," from lower (adj.), from Middle English lahghere (c. 1200), comparative of low (adj.). Transitive meaning "to let down, to cause to descend" attested from 1650s. Related: Lowered; lowering. In the sense "to cause to descend" the simple verb low (Middle English lahghenn, c. 1200) was in use into the 18c.[lower etymology, lower origin, 英语词源]
lower (v.2)youdaoicibaDictYouDict
"to look dark and threatening," also lour, Middle English louren, luren "to frown" (early 13c.), "to lurk" (mid-15c.), from Old English *luran or from its cognates, Middle Low German luren, Middle Dutch loeren "lie in wait." Form perhaps assimilated to lower (1). Related: Lowered; lowering.
lower (adj.)youdaoicibaDictYouDict
c. 1200, lahre, comparative of lah (see low (adj.)).