WordNet sense 1 (something determined in relation to something that includes it):

component, portion, component part

WordNet sense 2 (assets belonging to or due to or contributed by an individual person or group):

percentage, share

WordNet sense 3 (a portion of a natural object):

piece

WordNet sense 4 (the extended spatial location of something):

region

WordNet sense 5 (the melody carried by a particular voice or instrument in polyphonic music):

voice

WordNet sense 6 (an actor's portrayal of someone in a play):

character, persona, role, theatrical role

WordNet sense 7 (one of the portions into which something is regarded as divided and which together constitute a whole):

division, section

WordNet sense 8 (a line of scalp that can be seen when sections of hair are combed in opposite directions):

parting

WordNet sense 9 (discontinue an association or relation; go different ways):

break, separate, split, separate, break up, split up

WordNet sense 10 (leave):

depart, start, set forth, take off, set off, set out, start out

WordNet sense 11 (come apart):

divide

WordNet sense 12 (force, take, or pull apart):

disunite

WordNet sense 13 (any one of a number of individual efforts in a common endeavor):

contribution

WordNet sense 14 (the actions and activities assigned to or required or expected of a person or group):

function, office

WordNet sense 15 (in part; in some degree; not wholly):

partially, partly