helix
Helix is singular. Helices is plural.
The plural of helix is helices.
Bacterium is the singular word.
the singular word it is salmon.
singular
Adenoma is the singular of adenomata.
The word 'Phenomenon' is singular. The plural form is 'Phenomena'.
The singular form of the word flagella is flagellum.
singular of the word stitches is stitch.
Lance is singular.
The word "hang" is singular.
Yes, the word "document" is singular.