Siansa (sometimes anglicised as shanachy) describes an aesthetic ideal in Irish musical culture — the beauty that arises when multiple elements of sound come together in harmony. In poetry the term invokes this model of harmonious combination as a standard for lyric achievement: the poem as siansa balances sound, rhythm, and meaning into a unified whole. The word connects individual poetic craft to the communal music-making of Irish tradition, suggesting that the finest verse shares the quality of well-performed ensemble music. Revival poets drawn to the idea of Celtic harmony — a counter to what they saw as modern discordance — found siansa a useful touchstone.

Siansa (harmony/symphony) in Irish poetry describes a pleasing concert of sounds, whether musical or natural. It evokes a sense of order, beauty, and peace. Poets use siansa to depict the ideal state of relationships or environments. It contrasts with discord and chaos, representing balance. Siansa can refer to the harmony of voices in choir or the sounds of nature. Understanding siansa helps appreciate the aesthetic ideals of Irish poetry, where sound and meaning align to create unity.