The term RELATING TO SONGBIRDS can be broken down into two crossword solutions: OSCINE and PASSERINE. OSCINE is a 6-letter word meaning 'pertaining to or characteristic of certain singing birds of the suborder Oscines, which includes most songbirds.' Passerine is a 9-letter word meaning 'pertaining to or characteristic of the order Passeriformes, which includes most perching birds, such as sparrows, finches, and warblers.' Both terms refer to birds that are known for their singing abilities.