amhas m. [ˈãvəs̪] ‘gannet’, gen. amhais [ˈãviʃ] (cf. sùlaire). This word and its derivative amhsan m. [ˈãũs̪an] have been derived from ON *hálsa vb. (leg. halsa, with a short stressed vowel) ‘to clew up sail’ (Henderson 1910, 127–28 
So also McDonald 2009, 361.
): the forms tabhs, amhas and amhsan (≈ibid.) are said to represent SG *abhsa, hence the derivation from ON halsa; the reference is seen to be to the gannet’s closing its wings when circling in the air. MacBain 1896 wonders whether amhas might be from Lat. anser ‘goose’, but this seems insupportable.
As Lockwood (1976, 275–76) notes, SG amhas is more likely to derive straightforwardly from EG aṁus, also aṁsa, m. ‘hireling, servant, attendant; hired soldier, mercenary’: EG aṁus gives SG amhas regularly (Morvern, Mull (Henderson ibid.)), which gives amhsan (Kintyre (Henderson ibid.; Faclan bhon t-Sluagh˄) and emhsan (sic) (Harris, Scalpay (Faclan bhon t-Sluagh˄)) with the addition of the nominally diminutive suffix -an (EG -án) and concommitant syncope, while tamhas (if it occurs) and tamhsan (Dwelly) arise from the attraction of the t- of the radical masculine article (an t‑amhas etc.).
Besides amhsan and the variant spelling form ansan, MacBain 1896 cites a dialectal form osan. Is this for *onsan, *omhsan, showing a ~ o alternation?
The form tabhs, which Henderson quotes from Forbes (1905, 37), is uncertain: it may represent an apocopated form of *tabhsa, with medial bh for mh under the influence of an tabh ‘the ocean (the Atlantic Ocean)’ and/or tàbh ‘hand-net’, q.v.; Henderson mistakenly notes that Forbes acquired his form from Caraid nan Gàidheal (i.e. the Rev. Tormod MacLeòid (Norman MacLeod) 1783–1862), but in this instance Forbes is citing the gannet’s nickname caraid nan Gàidheal ‘the friend of the Gaels’ 
Because the gannet’s distinctive dive was an indication of where fish could be found (Moireasdan 1952, 15).
. SG amhas and its derivatives have several extended senses, including ‘wild man, madman, idiot, blundering fool’ (MacLennan 1925), and Lockwood (ibid.) suggests ‘fool’ might be relevant in relation to the bird: ‘[a]ccording to widespread tradition, the gannet can be caught by nailing a herring to a floating board, onto which the foolish bird then plunges, killing itself on impact ...’, although the earlier senses ‘servant, attendant’, in terms of indicating the presence of fish and/or of accompanying a boat, seem plausible and tie into the sense of the nickname caraid nan Gàidheal.
As a variant of amhas, MacLennan cites amhasg, with inorganic -g; cf. John MacCodrum (p. 32, line 475): tamhasg ‘blockhead, wild man’, whose editor Matheson (1938, 372) compares Ir. tamhas ‘phantom’ and amhas ‘mercenary, wild fellow, glutton, monster’ (cf. Dinneen 1947), although tamhas should probably read támhas, cf. EG táṁaid ‘dies’, and is therefore probably not relevant, and note a potential source for tamhasg in EG taṁasc m. ‘dwarf’ (eDIL˄).
Derivatives: amhasag f. ‘foolish woman’ (Dwelly 1911), with the suffix -ag (EG -óc).