a louse // many lice

a sheep // many sheep
a deer // many deer
an elk // many elk
a moose // many moose

a wolf  // many wolves
a knife // many knives
a wife // many wives

a man // many men
a woman // many women

a goose // many geese
a foot // many feet
a tooth // many teeth

a series / many series
a crossroads // many crossroads

a basis // many bases
an oasis // many oases
an analysis // many analyses
a crisis // many crises
a hypothesis //  many hypotheses
in the early 1990s
in the mid-1990s
in the late 1990s

in the 14th century = in the 1300s

in the early 18th century = in the early 1700s
in the mid-18th century = in the mid-1700s
in the late 18th century = in the late 1700s

asleep: I was asleep.
awake: We were awake.
ashamed: I was ashamed of my behaviour.
ajar: The door is ajar.
aghast: She winced, aghast at his cruelty.
ablaze: His clothes were ablaze. = burning fiercely

pride oneself on s-g: he prided himself on his success.
make oneself at home: Make yourself at home.
defend oneself: I'll have to defend myself.

insecticide
fungicide
homicide
genocide: Slobodan Milosevic was accused of genocide.
spermicide
suicide: Hitler committed suicide.