What is the meaning of U-?

Alternative form of μ-; abbreviation of micro-.

alternative form of b-, appearing before consonants

I

marks the second-person plural subject on a verb

Used to form physical nouns from verbs.

you singular (used for conjugating verbs to the subjective or nominative case of the personal pronoun)

alternative form of mu-

Class 14 noun prefix.

you, thou; second-person singular subject concord.

Class 1a noun prefix.

he, she, it; class 1 subject concord.

he, she, it; class 3 subject concord.

Class 11 noun prefix; form of ulu- used before stems of more than one syllable.

un-, im-

an abbreviation of certain words beginning with "u"

un- (not)

used to create an undesired version of the following noun

used to strengthen/intensify the following noun

an abbreviation of certain words beginning with "u"

perfective prefix

you, thou; second-person singular subject concord.

he, she, it; class 1 subject concord.

he, she, it; class 3 subject concord.

Infinitive prefix.

Forms perfective verbs with the following meanings:

1. (no change in meaning)

   (no change in meaning)

   away

   to make a mistake while

   you, thou; second-person singular subject concord.

   he, she, it; class 1 subject concord.

   he, she, it; class 3 subject concord.

   you, thou; second-person singular subject concord.

   he, she, it; class 1 subject concord.

   he, she, it; class 3 subject concord.

   Third person singular subject + third person duoplural object.

   Marks the irrealis mood

   Class 14 noun prefix.

   2nd person singular subject concord.

   Allomorph of y- (first-person prefix) used for stems that begin with two consonants and have a first vowel u.

   With following vowel lengthened if in an unreduced open syllable.

   combining form of ur (“water”)

   2nd person singular subject concord. Translates as thou, you singular or informal.

   Class 3 subject concord.

   Class 14 subject concord.

   Class 14 noun prefix.

   Class 1 pronominal concord.

   (away) from

   (inchoative)

   (telicity)

   added to mean a bit

   (u- + imperfective base + se) intensification: until exhaustion, expressing final stage of a process. (collocates with k smrti (“to death”))

   (on perfective verbs) unintentionally, inadvertently, by mistake

   (root modality) [i.e., deontic + dynamic modality: ability, obligation, permission, readiness]

   to gain by activity

   in-, un-, non-; (prefix meaning not, reversing the meaning)

   dual and plural prefix added to certain verbs

   Rōmaji transcription of う

   appears in front of some verbs meaning: to make something behave in a certain way, en-, be-, make

   perfective prefix

   added to mean "a bit"

   added to mean away

   added to mean successfully, often without an imperfective counterpart

   Class 14 noun prefix.

   u class_(XI) noun prefix, denoting natural objects, extensions, abstract qualities, or collections of small things.

   -ness, -ity

   forms names of countries

   you, 2nd person singular subject concord

   it, m class_(III)/u class_(XI) subject concord

   verb-initial form of -u- (“it, m class_(III)/u class_(XI) object concord”)

   2nd person singular subject concord. Translates as thou or you (singular or informal).

   Class 14 noun prefix.

   you, thou; second-person singular subject concord.

   Class 1a noun prefix.

   he, she, it; class 1 subject concord.

   he, she, it; class 3 subject concord.

   Class 11 noun prefix; form of ulu- used before stems of more than one syllable.

   abstract or instrument nominalizing prefix

   non-gerundive nominalizing prefix

   you, thou; second-person singular subject concord.

   Class 1a noun prefix.

   he, she, it; class 1 subject concord.

   he, she, it; class 3 subject concord.

   Class 11 noun prefix.

   Source: wiktionary.org