Learn English – a word called that has more than one syllable

I would suggest project manager or project leader. They suggest that this person is in charge of the work being done, not necessarily the people doing it (except with regards to the actual tasks involved in the project).

EDIT:
These terms could also suggest that you and your "boss" are actually complete equals, but that your "boss" is taking the lead on this particular project (whereas you are in charge of other ventures, where this "boss" would submit to your authority on related matters).

Though I am disgusted at the Greek-Latin lexical miscegenation, a parent of multiple children is polyprogenitive, from the Latin prōgeniēs, 'to beget'. From The Embodied Female:

Co-wives and surrogacy exist since Biblical times. For instance, resenting the four sons her fertile sister “gave” their common husband Jacob, barren Rachel gives him her maid Bilhah as surrogate, and adopts the two sons by this union. Emotions driving these transactions are unaccounted by Freudian chains of phallocentric symbolic equations slip-sliding between baby = penis or Darwinian notions of polyprogenitive male desire to spread his sperm. Neither can egg-exchange be entirely construed by Kleinian gynaecratic accounts of reparative urges to undo unconscious phantasies of raiding the archaic mother's envied fertile body for the babies within.

Technically, and although it doesn't fit the poly- mold requested, a person with more than one child would be multiprogenic (or multi-progenic). (The Greek equivalent, as Janus pointed out, is polytecnic, from τέκνον meaning 'child, son'.)

Similarly, a person who has children with multiple partners, according to social scientists, practices multipartnered fertility.