#18 Oasis
Everyone knows about oasis in deserts,can you guess the plural of it.

#17 Oases
People call it oases.

#16 Nucleus
Nucleus is the core of cells.What about its plural?

#15 Nuclei
Plural of nucleus is nuclei.

#14 Larva
Single juvenile without any company is larva.

#13 Larvae
Larva in company of another larva together called as larvae.

#12 Phenomenon
Impressive and extraordinary,that's phenomenon for you.

#11 Phenomena
When two many phenomenon occurs simultaneously,that's phenomena for you.

#10 Deer
A Deer is roaming in the jungle.

#9 Again Deer
It is unusual but plural of deer is deer only,tricky one indeed.

#8 Roof
Everybody loves roof of their house.

#7 Rooves
When you see more than one roof all over the place then it is said as rooves.

#6 Goose story
We all have heard the story of the goose that laid the golden eggs.

#5 Too many goose
And when there are too many of goose then you have refer them as geese.

#4 Moose
Moose is the largest extant species in the deer family.

#3 Moose
And well plural of moose is not meese, it is moose again.

#2 Crisis
What crisis means to you,a situation full of problems.

#1 Crises
When too many crisis situation arises at once, then it becomes crises.