v1.0
Publishing history:
v1.0: 12/03/26
toirp f. [t̪ʰɔɾ̥ʲp], gen. idem, in the sense ‘sod’ and tarp m. [t̪ʰaɾ̥p], gen. tarpa -[ə], in the sense ‘clod, lump’ are derived from ON torf nt. ‘turf, sod’ by MacBain (1896; 1911, s.vv. tarp, toirp), also Henderson (1910, 117, s.v. tarp), MacLennan (1925, s.vv. tarp, toirp; so also Stewart 2004, 415, s.v. tarp, 416, s.v. toirp) and McDonald (2009, 423). There are a number of variants: tarp ~ torp, with a ~ o alternation (A); tairp ~ toirp, from an oblique case form (B); and tarpan ~ torpan, with the nominally diminutive suffix -an -[an] (C):
A 1. SG tarp
Shaw 1780: ‘clod, lump’; MacFarlane 1815: ‘idem’; Armstrong 1825: ‘clod, lump of earth or clay’; HSS 1828: ‘clod, lump’; MacBain 1896; 1911: ‘idem’; Dwelly 1911: ‘clod, lump of earth or clay’; MacLennan 1925: ‘clod, lump’; Wentworth 2003a, s.v. clay: ?tarp ‘human clay, human body’; 
?Through confusion with SG corp ‘body, carcase (in distinction to soul); corpse’ (Dwelly 1911).
A 2. SG torp
Faclan bhon t-Sluagh˄: ‘torp, tuirp 
Whether tuirp is an alternative form of or an inflected form of torp is not specified.
B 1. SG tairp
Dwelly 1911: see tarp.
B 2. SG toirp
Lhuyd 1700, 196: XXVII.12: a turf ‘toirp’ (Argyllshire); McAlpine 1832: ‘sod, divot; thick person’; MacBain 1896; 1911: ‘sod’; MacEachen 1906: ‘turf, sod’; Dwelly 1911: ‘idem’; MacLennan 1925: ‘divot, sod, turf’; AFB˄: ‘idem’.
C 1. SG tarpan
Shaw 1780: ‘cluster’; Mac Farlan 1795: ‘idem’; MacFarlane 1815: ‘idem’; Armstrong 1825: ‘idem’, ‘little clod’; HSS 1828: ‘cluster’; Dwelly 1911: ‘cluster; little clod’; AFB˄: ‘small clod, small lump of earth’.
C 2. SG torpan
Dwelly 1911: see tarpan; AFB˄: ‘small clod, small lump of earth’.
ON torf (in final -[v]) would formally be expected to yield SG *[t̪ʰɔɾ͡ɔv] or similar. SG toirp etc. is no doubt related to Ir. torpa ‘a clump, clod’, 
For example, cf. Lhuyd 1707: tarp ‘clod’, tarpán ‘cluster’; O’Brien 1768: tarp ‘clod, lump’, tarpán ‘cluster’; O’Reilly 1817: tarp ‘clod, lump’, tarpán ‘cluster’; Ó Dónaill 1977: tarp = torpa; torp, torpa ‘clump, clod; lumpish thing’; tarpán = torpán; torpán ‘clump, clod; roundish thing, lumpish person, pot-bellied person’ (var. torpachán); toirpín ‘lumpish thing; small thickset person; porpoise’ (var. tóirpeachán, tóirpín). (?Cf. torbán ‘tadpole’ (Ó Dónaill 1977), but which otherwise probably goes back to EG dorb ‘small insect or worm, esp. one that lives in water’ (eDIL˄), hence Ir. doirb ‘water beetle’ (Ó Dónaill), (West Donegal) doirbín ‘tadpole’ (pers. comm. Seòsamh Watson), SG doirb ‘unspecific term for a small/tiny/insignificant creature (e.g. small fry, minnow, worm, leech, small person)’, doirbeag ‘unspecific term for small wriggling animals (esp. minnows, tadpoles, fry, worms)’ (AFB˄).)
SG torpan ‘crab’ (Shaw 1780; Mac Farlan 1795: tàrpan; MacFarlane 1815: tarpan; Armstrong 1825: idem; HSS 1828: idem; Dwelly 1911: idem; AFB˄: torpan, tarpan) and Ir. tarpán (Lhuyd 1707, listed under to-; O’Reilly 1817) and torpán ‘idem’ (O’Brien 1768; Dinneen 1927) are considered to be corruptions of partan and portán (partán), respectively (O’Brien 1768, s.v. torpán; Vendryes 1996, s.v. idem).
Derivatives: compare, for example, SG tarpach adj. ‘cloddy, bulky, weighty’, tarpanach adj. ‘cloddy’, tarpachd f. ‘bulkiness’ (Armstrong 1825), toirpeanta adj. ‘squat, thick’ (MacLennan 1925) and torpach, tarpach adj. ‘bulging, bulky’ (Faclan bhon t-Sluagh˄).