"mono" means one, "di" means two, "mer" means parts, Therefore monomers have1 part. while dimers are made of 2 parts.
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer. examples: carbohydrate- glucose nucleic acid- nucleotide protein- amino acid lipid: a saturated or unsaturated fat molecule .
A dimer is a molecule consisting of two identical simpler molecules. examples: carbohydrate- sucrose lipid- phospholipid