What is the meaning of W-?

Alternative form of o-

indicates motion inside or inward

indicates motion upward

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

Obligatorily marks derivations of intransitive verbs adverbialized with -e or nominalized with any marker.

Marks a transitive verb as having a first-person agent/subject when the patient/object is of third person.

Marks an intransitive verb with agent-like argument or (with certain vowel-initial verbs) patient-like argument as having a first-person argument/subject with verb forms that take series I markers.

With following vowel lengthened if in an unreduced open syllable.

indicates motion inside or inward

indicates motion upward

u class(XI) noun prefix used before vowels

Source: wiktionary.org