In my leisurely cruise through Moby-Dick, I have reached Chapter 87, “The Grand Armada,” and I enjoyed this lexicographical footnote so much I thought I’d pass it on. The footnoted sentence reads, “Stripped to our shirts and drawers, we sprang to the white-ash, and after several hours’ pulling were almost disposed to renounce the chase, when a general pausing commotion among the whales gave animating token that they were now at last under the influence of that strange perplexity of inert irresolution, which, when the fishermen perceive it in the whale, they say he is gallied.” Whereto the following is appended:
*To gally, or gallow, is to frighten excessively, – to confound with fright. It is an old Saxon word. It occurs once in Shakspere: –
The wrathful skies
Gallow the very wanderers of the dark
And make them keep their caves.
Lear, Act III. sc. ii.
To common land usages, the word is now completely obsolete. When the polite landsman first hears it from the gaunt Nantucketer, he is apt to set it down as one of the whaleman’s self-derived savageries. Much the same is it with many other sinewy Saxonisms of this sort, which emigrated to the New-England rocks with the noble brawn of the old English emigrants in the time of the Commonwealth. Thus, some of the best and furthest-descended English words – the etymological Howards and Percys – are now democratised, nay, plebeianised – so to speak – in the New World.
The OED defines it as “To frighten, daze, scare, startle. Now  only dial. and in the whale fishery”; the citations are:
1608 Shakespeare King Lear ix. 44 The wrathfull Skies gallow, the very wanderer of the Darke, and makes them keepe their caues.
1700 Let. 8 Apr. in T. Brown 3rd Vol. Wks. (1708) ii. 102 The People look’d as if they were gallied.
1823 New Monthly Mag. 7 231 We were one and all mortally gallied at the sight.
1840 F. Marryat Poor Jack vi. 29 They [sc. bull whales] are..easily ‘gallied’, that is, frightened.
1874 C. M. Scammon Marine Mammals N. Amer. iii. iii. 227 The whale is approached in the most cautious manner, to avoid ‘gallying’ it.
1883 W. H. Cope Gloss. Hampshire Words ‘Galley them pigs out o’ the peasen.’
1888 F. T. Elworthy W. Somerset Word-bk. Gally, to frighten. (Very common.)
Alas, it hasn’t been updated, so the only etymology is “Old English a-gælwan to alarm.”