(verb)
to carelessly mark or stain a surface with a greasy, sticky, or dirty substance;
e.g. The children used their hands to smear mud onto their faces.
(verb)
to smudge or obscure something (such as text), or to blur or wipe out the outline of something;
e.g. The ink will smear if you touch it before it dries.
(verb)
to damage or sully someone's reputation by making false accusations against them or spreading false charges about them;
e.g. His colleague tried to smear him by suggesting that he had falsified the results of his experiments.
(noun)
a spot or streak of a sticky, greasy, or dirty substance;
e.g. A smear of oil clouded the lens of his glasses.
(noun)
a preparation made for medical diagnosis that involves a sample of a bodily substance (e.g. tissue or fluid) spread onto a microscope slide for examination;
e.g. The doctor prepared a smear of her throat to diagnose her infection.
(noun)
an unproved accusation or false charge made against a person or entity in order to damage/destroy their reputation;
e.g. Her statement is clearly a smear against her opponent.