What is the meaning of Y-?

Used with past participle conjugations to form past participles (this prefix does not occur independently and is no longer productive).

Used together with the suffix -i to create masculine agent nouns.

he or she (used for conjugating verbs to the subjective or nominative case of the personal pronoun)

Added to verbs as a perfective prefix or intensifier.

Used to form nouns of association similar to English co-.

Used with past participle conjugations to form past participles.

Form used before a verb affixed with -a- or subjunctive -e- of a-

Form used before a verb affixed with -a- or subjunctive -e- of e-

Marks a noun as having a first-person possessor.

Marks a postposition as having a first-person object.

Marks a transitive verb as having a first-person patient/object when the agent/subject is of third person with verb forms that take series I markers.

Marks a transitive verb as having a first-person patient/object when the agent/subject is unspecified with verb forms that take series II markers.

Marks an intransitive verb with patient-like argument as having a first-person argument/subject with verb forms that take series I markers (excepting a few verbs that take w-) and on all intransitive verbs with verb forms that take series II markers.

Marks a verb form derived with n- and -dü or -'jüdü as having a first-person agent/subject.

With following vowel lengthened if in an unreduced open syllable.

Marks a noun as having a third-person possessor.

Marks a postposition as having a third-person object.

Marks a transitive verb as having a third-person patient/object with verb forms that take series II markers.

Marks an intransitive verb as having a third-person argument/subject with verb forms that take series II markers.

Marks a verb as having third-person arguments when marked with the admonitive -'no, prohibitive -i, or uncertain future -tai suffixes.

With following vowel lengthened if in an unreduced open syllable.

A marker for the third person object

A peg element added to 1st person plural ∅-imperfective verbs to fit syllable shape restraints

Source: wiktionary.org