Definition of "tairn"

Thou Wind, that ravest without, / Bare craig, or mountain-tairn, or blasted tree, / Or pine-grove whither woodman never clomb, / Or lonely house, long held the witches' home, / Methinks were fitter instruments for thee, / Mad Lutanist! [footnote: Tairn is a small lake, generally if not always applied to the lakes up in the mountains, and which are the feeders of those in the valleys. […]]

1802 October 4, S[amuel] T[aylor] Coleridge, “Dejection: An Ode”, in The Morning Post; republished in Henry Nelson Coleridge, editor, The Poetical Works of S. T. Coleridge, volume I (Juvenile Poems; Sibylline Leaves), London: William Pickering, 1834, stanza VII, page 239