As nouns the difference between louse and leech
is that
louse is a small parasitic wingless insect of the order
phthiraptera while
leech is an aquatic blood-sucking annelid of class hirudinea, especially or
leech can be (archaic) a physician or
leech can be (nautical) the vertical edge of a square sail.
As verbs the difference between louse and leech
is that
louse is to remove lice from the body of a person or animal; to delouse while
leech is to apply a leech medicinally, so that it sucks blood from the patient.