lower
v.
1
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.
2
"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.
adj.
c.1200, lahre, comparative of lah (see low, adj.).