WordNet sense 1 (a shape that is spherical and small):

bead, pearl

WordNet sense 2 (a small indefinite quantity (especially of a liquid)):

driblet, drib

WordNet sense 3 (a steep high face of rock):

cliff, drop-off

WordNet sense 4 (a free and rapid descent by the force of gravity):

fall

WordNet sense 5 (a sudden sharp decrease in some quantity):

dip, free fall

WordNet sense 6 (a curtain that can be lowered and raised onto a stage from the flies; often used as background scenery):

drop curtain, drop cloth

WordNet sense 7 (hang freely):

dangle, swing

WordNet sense 8 (stop associating with):

dismiss, send packing, send away

WordNet sense 9 (pay out):

expend, spend

WordNet sense 10 (fall or drop to a lower place or level):

sink, drop down

WordNet sense 11 (let or cause to fall in drops):

dribble, drip

WordNet sense 12 (get rid of):

cast, shed, throw, cast off, shake off, throw off

WordNet sense 13 (leave or unload, especially of passengers or cargo):

discharge, unload, discharge, drop off, set down, put down

WordNet sense 14 (cause to fall by or as if by delivering a blow):

fell, cut down, strike down

WordNet sense 15 (leave undone or leave out):

miss, neglect, omit, overlook, overleap, pretermit, overlook, leave out

WordNet sense 16 (lower the pitch of (musical notes)):

flatten

WordNet sense 17 (stop pursuing or acting):

knock off

WordNet sense 18 (grow worse):

degenerate, deteriorate, devolve, degenerate