Possessive suffixes

Singular	Meaning	Plural	Meaning
-enin	My	-emen	Our
-egen	Your (informal)	-egenir	Your (informal)
-elen	Your (formal)	-edenir	Your (formal)
-ed	His/her/its	-ent	Their

These suffixes can be added to any word, even if it ends with a vowel.

What is a possessive suffix?
A possessive suffix is an alternative to using the possessive pronouns in Lesson 16, where instead of surrounding the word with the pronoun, the ending is attached to the word.
Attested words with possessive suffixes in Sindarin include:
lammen = my tongue (from Gandalf's invocation outside Moria, 'lasto beth lammen')
guren = my heart

If Gandalf said 'lammen', why does the table above indicate it should be 'lammenin'?
This is a very good question, and if you own a copy of PE17 I will refer you to page 46.
It seems that Tolkien considered there to be 'older Sindarin' versions of these suffixes, which includes the -en seen in the Lord of the Rings. The table above shows the 'newer Sindarin' equivalents that Tolkien wrote down.

Examples
Hervenned = Her husband
Nanethegen = Your mother
Hûemen = Our dog
Ionent = Their son

-eg/-ig

The suffixes -eg/-ig in Sindarin have three uses. They are used as a diminutive suffix, a singular suffix and an extension of the diminutive ending -y in English where we neither want nor need to be precise about a meaning.

-eg and -ig are interchangeable. You may use whichever one you prefer and think fits the word and sounds best.

Use as a diminutive suffix

A diminutive conveys a sense of smallness or of intimacy and endearment. In English we often use diminutive suffixes on names to indicate closeness such as Freddy instead of Fred/Alfred, or Kitty/Cathy instead of Catherine.
In Sindarin you could use this to mean 'my (little) ___' or as a nickname to indicate informality.

Examples
Atheg = Little father (play name for the thumb)
Emig = Little mother (play name for the index finger)
Nogotheg = Dwarflet (another name for the Petty Dwarves)

Use as a singular suffix

A singular suffix indicates there is just one of whatever it is. Unlike the normal singular forms (e.g. Carab = a hat) these exist because the usual word indicates plurality. For instance you wouldn't need to write Lebereg = A single finger because Leber already indicates this.

Examples
Gwanunig = A single twin from Gwanûr/Gwenyn = Pair of twins
Lheweg = An ear from Lhaw = Pair of ears
Lotheg = A single flower from Loth = A flower, head of small flowers

Impreciseness '-ish'

Quenya's diminutive suffix -incë is the direct cognate of -eg/-ig and is used to create the word luinincë = bluish.
As the English diminutive suffix -y can be used for much the same purpose (bluey, reddy) I propose that -eg/-ig can be added to Sindarin colour words.

Examples
Luineg = Bluish
Caraneg = Reddish
Malenig = Yellowish