The article deals with the issue of differentiation of outer homonyms: compound terms and subject phraseological units. As the objective criterion of differentiation of homonymic units of this type there are considered the morphological differences: phraseological units and compound terms differ in character, expression form and functioning of grammar categories. The absence of some grammar forms, the presence of high-frequency and rarely used forms is the consequence of the phraseological meaning and the means of differentiation of phraseological units and terms.