v2.0
Publishing history:
v1.0: 15/06/25
v2.0: 15/10/25: Scots crappit-heid reference added.
ceann-gropaig m. [̩̩ kʲʰãũᵰ̪ ˈɡ̊ɾɔʰpiɡ̊ʲ] ‘a boiled fish head stuffed with a mixture of oatmeal and fish liver’ is derived by Mackenzie (1910, 384, s.v. ceann gropig [sic]) from SG ceann ‘head’ + ON grjupa [sic] ‘a sausage’ (cf. OIce. grjúpan nt. (Cleasby 1874) and ON grúpan nt. ‘idem’ (NO)). Christiansen (1938, 4: ceann gropig, Lewis, but 17–18: ceanngropidh) suggests that an association with Scots (Shetland) kroppin ‘idem’ (Jakobsen 1928) is more likely (see below). McDonald (2009, 359) considers the loan uncertain. ON grúpan is unlikely to yield short SG [ɔ]. The second element of SG ceann-gropaig has a number of forms, with a variety of initials and with a variety of endings.
Forms are sometimes spelt without a hyphen, but a hyphen is used throughout below.
A 1. SG ceann-cropaig
(i) ceann-cropaig (Matheson in CG VI, 17, s.v. bonnach-gropaidh; AFB˄: Lewis, Harris, Skye; Faclan bhon t-Sluagh˄: with cròpaig corrected to cropaig);
(ii) ceann-cropaic (Faclan bhon t-Sluagh˄: Lewis), for ceann-cropaig;
(iii) ceann-crapaig (AFB˄), ?with a ~ o alternation in Gaelic;
(iv) ceann-cnapaig (Dwelly App.: Caithness, Sutherland, Lewis), ?with nasalisation spread from the initial element of the compound (cf. Ó Maolalaigh 2003a, 114).
A 2. SG ceann-cropaidh
(i) ceann-cropaidh (Dwelly App.: Wester Ross, Hebrides; AFB˄: Skye, Sutherland);
(ii) ceann-chropaidh (Faclan bhon t-Sluagh˄: Sutherland), with lenition of the second element probably from an oblique-case form.
A 3. SG ceann-cropach
In AFB˄: Harris.
B 1. SG ceann-gropaig
In Dwelly App. as ceann-gropaig, but in Mackenzie 1910, 384, and Christiansen 1938, 4: Lewis, misspelt as ceann-gropig.
B 2. SG ceann-gropaidh
In CG VI, 17, s.v. bonnach-gropaidh, Christiansen 1938, 17–18: Lewis, and in Faclan bhon t-Sluagh˄: Skye.
B 3. SG ceann-gropach
In Faclan bhon t-Sluagh˄: Harris.
C. SG ceann-propaig
In Matheson in CG VI, 17, s.v. bonnach-gropaidh, and in Dwelly App.
The second element of SG ceann-cropaig etc. is probably a loan from Scots crappen, kroppin, cropping etc. ‘idem’, 
SND˄, s.v. crappen etc.: ‘[m]eal and fish-livers crushed together, meal-dumplings, filled with fish-livers. Mostly in the form kroppin and esp[ecially] denoting meal and fish-livers crushed together, stuffed into the head of a fish, and boiled’ (also in the compound crappen head), probably from Scots crap ‘to fill, stuff, cram’ (ibid.). Cf. Scots crappit heid ‘stuffed head’ (with the past participle of crap), with which Duncan (1995, 94) translates ceann-cropaig: ‘[a]lthough ceann cropaig, or ‘crappit heids’ [sic], were known in Scarp, I do not remember it as a meal, but I have enjoyed it several times in a crofter’s home in Coll, near Stornoway, where my mother-in-law was brought up. It was made from the stuffed heads of fresh haddock from Broad Bay’ (quoted in SND˄, s.v.).
Alternatively in the case of ceann-gropaig, c- is conceivably voiced following the nasal of ceann, cf. (although all with first syllable stress) seann-taigh with [dh]- (Wentworth 2003, s.v. house (old) : Gairloch), seann-talamh [d]-, Seann-Tiomnadh [dj]- (Dieckhoff 1932: Glengarry).