This is a Scottish term but its first meaning is like the English word full:
fou (comparative more fou, superlative most fou)
The definition below is from the Dictionary of the Scots Language. It is authoritative and definitive. (Downvote at your own risk.)
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FOU, adj., adv., n., v. Also fu', foo(e), †foue, †fow(e); †foul. Sc. forms and usages of Eng. full. See P.L.D. § 78 (3) and Full.
[Sc. fu:; s.Sc. fʌu]
There is an entire page of quotations, variations and citations.
I. adj. 1. As in Eng.
Edb. 1720 A. Pennecuik Helicon 78:
His Face was big and fair like a fow Moon.
Full of food, well-fed, sated, replete (ne.Sc., Ags., Fif., m.Lth., Bwk., Rxb. 1953). Also fig.
Full of liquor, drunk, intoxicated. Gen.Sc. Used also with bitch, blin, greetin, roarin, stottin, tumblin, etc. to indicate the degree or nature of the intoxication, and in many similes as fou as a buckie, a piper, a puggie, a wilk, the Baltic, the ee o' a pick (see Ee, n., 2. (2)), etc., etc., in some of which fou partly retains its meaning 1. Deriv. fouish, slightly drunk, tipsy (Edb. 1828 D. M. Moir Mansie Wauch (1898) ii.).
‡4. In comfortable circumstances, well-off, having plenty, well-provided (Rxb. 1923 Watson W.-B.); bountiful, open. Deriv. †fowie, id., gen. used with contemptuous force, implying miserliness (Rxb. 1825 Jam.).
- Combs.: (1) fou-han't (Cld. 1880 Jam.), -hannit (Bnff. 1866 Gregor D. Bnff. 224; Abd.27 1953), having the hands full, having a sufficiency; fully repaid or requited; (2) fou-hauden, -hadden, lavishly supplied, having no lack or scarcity, esp. of food (Rxb. 1923 Watson W.-B.); (3) fou-moot, having all the teeth in a sound state (Bnff. 1866 Gregor D. Bnff. 224). Eng. has full-mouthed, id., of cattle.
‡II. adv. Fully, very, quite; rather, too; with compar., much (Per., Fif., Lth., Ayr. 1915–26 Wilson; Ork., Cai., Abd., wm.Sc. 1953). Now arch. or dial. in Eng.
III. n. 1. A fill, the quantity that fills, the full capacity (Gall. 1824 MacTaggart Gallov. Encycl. 209; Sh., Cai., ne.Sc., Ags., Fif., Clc., Gall., Dmf., Uls. 1953), a full load; specif. of drink, as much as one can hold.
†2. In dry measure: a firlot or quarter boll, approx. = one imperial bushel of wheat or 1.4 of a bushel of barley or oats; “the full of a measure of potatoes, onions, etc. . . . This is always supposed to be heaped unless the term sleek be used, which is equivalent to straik or stroke” (Cld., s.Sc. 1825 Jam.); a vessel holding this amount. Also foul (Ayr. 1706 Arch. and Hist. Coll. Ayr. and Wgt. IV. 216). Cf. Full, n. 2., and half-fou, s.v. Half, adj., 1.
‡IV. v. To fill (Abd. 1825 Jam.), to load. Redupl. form foo-foo.
Gsw. 1877 A. G. Murdoch Laird's Lykewake 71:
Think o' yer wark! the greedy laird's foo-fooin' up the purse.
Fou is a variant form of the word foul in Scottish, which means unwashed or dirty: