Generally, when speaking of the vermiform appendix, the plural is appendixes; but when speaking of additional material added to a scholarly work or an official document, the plural is appendices.
Another word for a sports referee is an umpire.
The word crises is a plural word; it is the plural form of the word crisis.
Yes, as the plural of officer, meaning a person in a position of trust or authority. If you're looking for a word meaning to act in an official capacity, officiate is the word you need.
There is no plural word for if.
The plural form for the demonstrative pronoun this is these.
A non-plural word, a word (noun or pronoun) that is not plural is singular, a word for just one.
The plural word of delay is delays.
the plural word is comedones
No it's a singular word. A plural word would be "have".
Leukocytes is the plural of leukocyte
The plural of "classification" is "classifications."