from Edward Bunting, The Ancient Music of Ireland (Dublin 1840), page 20: The parts of the harp.
Irish an fhorshnaidhm
spoken by Gráinne Yeats
Scottish Gaelic an ursnaidhim spoken by Tony Dilworth
Click the play button to hear it spoken. help
It seems that An foirshnadhm refers to the wooden toggle, or possibly the knot made by the string around the toggle. The string is passed up through the small string-hole in the soundboard, and the toggle, pressing against the back of the soundboard, holds the string firmly in place.
Some modern harp players use metal rather than wooden toggles. This video shows the knot being wound around a metal toggle.
Video demonstration: Bill Taylor; Filming: Barnaby Brown
An foirshnadhm ('in English characters' Aufhoirshnadhaim) - The wooden pegs to which the strings are fastened.
This looks as if it might be for an fhorshnaidhm, an otherwise unknown compound of snaidhm (feminine), 'a knot', with the prefix for-, which usually adds implications of 'over, outer, great, extreme'. This is a singular noun, however ('the top knot' perhaps?), and cannot directly translate the English 'wooden pegs'. On p.30 the translation given is 'The pin board, or wooden pegs, to which the strings are fastened'; but see cor.
However, this entry is likely to be related to a garbled one on p.36: Uinaidhin ceangal, no ursnaidhm ceangal, 'The pin or jack that fastens the wire of the harp'. Though Bunting got this (in some form) from the 1792 harpers, the term urshnaidhm is probably that appearing in medieval literature as earsnaidm or airshnaidm (still a compound of snaidhm), apparently an equivalent of céis, a disputed term for some part of a harp. Urshnaidhm ceangail, 'an urshnaidhm of tying/binding', might accord reasonably well with Bunting's descriptions.
Colm Ó Baoill 2002