Answer:
The removal of a hydrogen from one monomer and the removal of a hydroxyl group from the other monomer allows the monomers to share electrons and form a covalent bond. Thus, the monomers that are joined together are being dehydrated to allow for synthesis of a larger molecule.
Many reactions involving dehydration synthesis are associated with the formation of biological polymers where the addition of each monomer is accompanied by the elimination of one molecule of water.